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Botnet

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A botnet is a collection of software agents, or robots, that run autonomously and automatically. The term is most commonly associated with IRC bots and more recently malicious software, but it can also refer to a network of computers using distributed computing software.[citation needed]

Background

The main drivers for botnets are for recognition and financial gain. The larger the botnet, the more ‘kudos’ the herder can claim to have among the underground community. The bot herder will also ‘rent’ the services of the botnet out to third parties, usually for sending out spam messages, or for performing a denial of service attack against a remote target. Due to the large numbers of compromised machines within the botnet huge volumes of traffic (either email or denial of service) can be generated. However, in recent times the volumes of spam originating from a single compromised host have dropped in order to thwart anti-spam detection algorithms – a larger number of compromised hosts send a smaller number of messages in order to evade detection by anti-spam techniques.

Botnets have become a significant part of the Internet, albeit increasingly hidden. Due to most conventional IRC networks taking measures and blocking access to previously-hosted botnets, controllers must now find their own servers. Often, a botnet will include a variety of connections and network types. Sometimes a controller will hide an IRC server installation on an educational or corporate site where high-speed connections can support a large number of other bots. Exploitation of this method of using a bot to host other bots has proliferated only recently.

Several botnets have been found and removed from the Internet. The Dutch police found a 1.5 million node botnet[1] and the Norwegian ISP Telenor disbanded a 10,000-node botnet.[2] In July 2010, the FBI arrested a 23-year old Slovenian held responsible for the malicious software that integrated an estimated 12 million computers into a botnet.[3] Large coordinated international efforts to shut down botnets have also been initiated.[4] It has been estimated that up to one quarter of all personal computers connected to the internet may be part of a botnet.[5]

Organization

While botnets are often named after their malicious software name, there are typically multiple botnets in operation using the same malicious software families, but operated by different criminal entities.[6]

While the term "botnet" can be used to refer to any group of bots, such as IRC bots, this word is generally used to refer to a collection of compromised computers (called zombie computers) running software, usually installed via drive-by downloads exploiting web browser vulnerabilities, worms, Trojan horses, or backdoors, under a common command-and-control infrastructure.

A botnet's originator (aka "bot herder" or "bot master") can control the group remotely, usually through a means such as IRC, and usually for nefarious purposes. Individual programs manifest as IRC "bots". Often the command-and-control takes place via an IRC server or a specific channel on a public IRC network. This server is known as the command-and-control server ("C&C"). Though rare, more experienced botnet operators program their own commanding protocols from scratch. The constituents of these protocols include a server program, client program for operation, and the program that embeds itself on the victim's machine (bot). All three of these usually communicate with each other over a network using a unique encryption scheme for stealth and protection against detection or intrusion into the botnet network.

A bot typically runs hidden and uses a covert channel (e.g. the RFC 1459 (IRC) standard, twitter or IM) to communicate with its C&C server. Generally, the perpetrator of the botnet has compromised a series of systems using various tools (exploits, buffer overflows, as well as others; see also RPC). Newer bots can automatically scan their environment and propagate themselves using vulnerabilities and weak passwords. Generally, the more vulnerabilities a bot can scan and propagate through, the more valuable it becomes to a botnet controller community. The process of stealing computing resources as a result of a system being joined to a "botnet" is sometimes referred to as "scrumping."

Botnet servers will often liaise with other botnet servers, such that a group may contain 20 or more individual cracked high-speed connected machines as servers, linked together for purposes of greater redundancy. Actual botnet communities usually consist of one or several controllers that rarely have highly-developed command hierarchies between themselves; they rely on individual friend-to-friend relationships.[citation needed]

The architecture of botnets has evolved over time, and not all botnets exhibit the same topology for command and control. Depending upon the topology implemented by the botnet, it may make it more resilient to shutdown, enumeration, or command and control location discovery. However, some of these topologies limit the saleability and rental potential of the botnet to other third-party operators.[7] Typical botnet topologies are:

  • Star
  • Multi-server
  • Hierarchical
  • Random

To thwart detection, some botnets were scaling back in size. As of 2006, the average size of a network was estimated at 20,000 computers, although larger networks continued to operate.[8]

Formation and exploitation

This example illustrates how a botnet is created and used to send email spam.

  1. A botnet operator sends out viruses or worms, infecting ordinary users' computers, whose payload is a malicious application—the bot.
  2. The bot on the infected PC logs into a particular C&C server (often an IRC server, but, in some cases a web server).
  3. A spammer purchases the services of the botnet from the operator.
  4. The spammer provides the spam messages to the operator, who instructs the compromised machines via the IRC server, causing them to send out spam messages.

Botnets are exploited for various purposes, including denial-of-service attacks, creation or misuse of SMTP mail relays for spam (see Spambot), click fraud, spamdexing and the theft of application serial numbers, login IDs, and financial information such as credit card numbers.

The botnet controller community features a constant and continuous struggle over who has the most bots, the highest overall bandwidth, and the most "high-quality" infected machines, like university, corporate, and even government machines.[citation needed]

Botnet lifecycle

  • Bot-herder configures initial bot parameters such as infection vectors, payload, stealth, C&C details
  • Register a DDNS
  • Register a static IP
  • Bot-herder launches or seeds new bot(s)
  • Bots spread
  • Causes an increase of DDoS being sent to the victim
  • Losing bots to rival botnets

Types of attacks

  • Denial-of-service attacks where multiple systems autonomously access a single Internet system or service in a way that appears legitimate, but much more frequently than normal use and cause the system to become busy.
  • Adware exists to advertise some commercial entity actively and without the user's permission or awareness, for example by replacing banner ads on web pages with those of another content provider.
  • Spyware is software which sends information to its creators about a user's activities – typically passwords, credit card numbers and other information that can be sold on the black market. Compromised machines that are located within a corporate network can be worth more to the bot herder, as they can often gain access to confidential information held within that company. There have been several targeted attacks on large corporations with the aim of stealing sensitive information, one such example is the Aurora botnet.[9]
  • E-mail spam are e-mail messages disguised as messages from people, but are either advertising, annoying, or malicious in nature.
  • Click fraud is the user's computer visiting websites without the user's awareness to create false web traffic for the purpose of personal or commercial gain.
  • Access number replacements are where the botnet operator replaces the access numbers of a group of dial-up bots to that of a victim's phone number. Given enough bots partake in this attack, the victim is consistently bombarded with phone calls attempting to connect to the internet. Having very little to defend against this attack, most are forced into changing their phone numbers (land line, cell phone, etc.).
  • Fast flux is a DNS technique used by botnets to hide phishing and malware delivery sites behind an ever-changing network of compromised hosts acting as proxies.

Preventive measures

If a machine receives a denial-of-service attack from a botnet, few choices exist. Given the general geographic dispersal of botnets, it becomes difficult to identify a pattern of offending machines, and the sheer volume of IP addresses does not lend itself to the filtering of individual cases. Passive OS fingerprinting can identify attacks originating from a botnet: network administrators can configure newer firewall equipment to take action on a botnet attack by using information obtained from passive OS fingerprinting. The most serious preventive measures utilize rate-based intrusion prevention systems implemented with specialized hardware.

Some botnets use free DNS hosting services such as DynDns.org, No-IP.com, and Afraid.org to point a subdomain towards an IRC server that will harbor the bots. While these free DNS services do not themselves host attacks, they provide reference points (often hard-coded into the botnet executable). Removing such services can cripple an entire botnet. Recently, these companies have undertaken efforts to purge their domains of these subdomains. The botnet community refers to such efforts as "nullrouting", because the DNS hosting services usually re-direct the offending subdomains to an inaccessible IP address. Similarly, some botnets implement custom versions of well-known protocols. The implementation differences can be used for fingerprint-based detection of botnets. For example, Mega-D features a slightly modified SMTP protocol implementation for testing the spam capability. Bringing down the Mega-D's SMTP server disables the entire pool of bots that rely upon the same SMTP server.[10]

The botnet server structure mentioned above has inherent vulnerabilities and problems. For example, if one was to find one server with one botnet channel, often all other servers, as well as other bots themselves, will be revealed. If a botnet server structure lacks redundancy, the disconnection of one server will cause the entire botnet to collapse, at least until the controller(s) decides on a new hosting space. However, more recent IRC server software includes features to mask other connected servers and bots, so that a discovery of one channel will not lead to disruption of the botnet.

Several security companies such as Afferent Security Labs, Symantec, Trend Micro, FireEye, Simplicita and Damballa have announced offerings to stop botnets. While some, like Norton AntiBot (discontinued), are aimed at consumers, most are aimed to protect enterprises and/or ISPs. The host-based techniques use heuristics to try to identify bot behavior that has bypassed conventional anti-virus software. Network-based approaches tend to use the techniques described above; shutting down C&C servers, nullrouting DNS entries, or completely shutting down IRC servers.

Newer botnets are almost entirely P2P, with command-and-control embedded into the botnet itself. By being dynamically updateable and variable they can evade having any single point of failure. Commanders can be identified solely through secure keys and all data except the binary itself can be encrypted. For example a spyware program may encrypt all suspected passwords with a public key hard coded or distributed into the bot software. Only with the private key, which only the commander has, can the data that the bot has captured be read.

Newer botnets have even been capable of detecting and reacting to attempts to figure out how they work. A large botnet that can detect that it is being studied can even DDoS those studying it off the internet.

There is an effort by researchers at Sandia National Laboratories to analyze the behavior of these botnets by simultaneously running one million Linux kernels as virtual machines on a 4,480-node Dell high-performance computer cluster.[11]

Historical list of botnets

Date created Name Estimated no. of bots Spam capacity Aliases
1999 !a 999,999,999 100000 !a
2009 (May) BredoLab 30,000,00030,000,000[12] 3.6 billion/day Oficla
2008 (around) Mariposa 12,000,000[13] 0 ? None
0? Conficker 10,000,000+[14] 10 billion/day DownUp, DownAndUp, DownAdUp, Kido
0? Zeus 3,600,000 (US Only) [15] -1n/a Zbot, PRG, Wsnpoem, Gorhax, Kneber
2007 (Around) Cutwail 1,500,000 [16] 74 billion/day Pandex, Mutant (related to: Wigon, Pushdo)
0? Grum 560,000 [17] 39.9 billion/day Tedroo
0? Mega-D 509,000 [18] 10 billion/day Ozdok
0? Kraken 495,000 [19] 9 billion/day Kracken, JoolzCheat
2007 (March) Srizbi 450,000[20] 60 billion/day Cbeplay, Exchanger
0? Lethic 260,000 [21] 2 billion/day none
2004 (Early) Bagle 230,000[21] 5.7 billion/day Beagle, Mitglieder, Lodeight
0? Bobax 185,000 9 billion/day Bobic, Oderoor, Cotmonger, Hacktool.Spammer, Kraken[citation needed]
0? Torpig 180,000 [22] -1 n/a Sinowal, Anserin
2006 (Around) Rustock 150,000 [23] 30 billion/day RKRustok, Costrat
0? Storm 160,000 [24] 3 billion/day Nuwar, Peacomm, Zhelatin
0? Donbot 125,000 [25] 0.8 billion/day Buzus, Bachsoy
2008 (November) Waledac 80,000 [26] 1.5 billion/day Waled, Waledpak
0? Maazben 50,000 [21] 0.5 billion/day None
0? Onewordsub 40,000 [27] 1.8 billion/day 0?
0? Gheg 30,000 [21] 0.24 billion/day Tofsee, Mondera
0? Nucrypt 20,000 [27] 5 billion/day Loosky, Locksky
0? Wopla 20,000 [27] 0.6 billion/day Pokier, Slogger, Cryptic
2008 (Around) Asprox 15,000 [28] 0 ? Danmec, Hydraflux
0? Spamthru 12,000 [27] 0.35 billion/day Spam-DComServ, Covesmer, Xmiler
0? Xarvester 10,000 [21] 0.15 billion/day Rlsloup, Pixoliz
2009 (August) Festi 0 ? 2.25 billion/day none
2008 (Around) Gumblar 0 ? 0 ? None
0? Akbot 0 ? 0 ? None
2100 z! -100,000,000 -99999 z!

See also

References

  1. ^ Botnet operation controlled 1.5m PCs by Tom Sanders, vnunet.com.
  2. ^ Telenor takes down 'massive' botnet by John Leyden, The Register.
  3. ^ "APNewsBreak: FBI says mastermind of botnet nabbed — Yahoo! News". News.yahoo.com. 2010-07-14. Retrieved 2010-07-30. [dead link]
  4. ^ ISPs urged to throttle spam zombies by John Leyden, The Register.
  5. ^ Criminals 'may overwhelm the web', BBC, 25 January 2007.
  6. ^ Many-to-Many Botnet Relationships, Damballa, 8 June 2009.
  7. ^ Botnet Communication Topologies, Damballa, 10 June 2009.
  8. ^ "Hackers Strengthen Malicious Botnets by Shrinking Them" (pdf). Computer. IEEE Computer Society. April 2006. Retrieved 2010-10-22. The size of bot networks peaked in mid-2004, with many using more than 100,000 infected machines, according to Mark Sunner, chief technology officer at MessageLabs...The average botnet size is now about 20,000 computers, he said. {{cite journal}}: More than one of |work= and |journal= specified (help)
  9. ^ "Operation Aurora — The Command Structure". Damballa.com. Retrieved 2010-07-30.
  10. ^ C.Y. Cho, D. Babic, R. Shin, and D. Song. Inference and Analysis of Formal Models of Botnet Command and Control Protocols, 2010 ACM Conference on Computer and Communications Security.
  11. ^ http://www.eweek.com/c/a/Security/Researchers-Boot-Million-Linux-Kernels-to-Help-Botnet-Research-550216/?kc=EWKNLLIN08182009STR2
  12. ^ Infosecurity (UK) - BredoLab downed botnet linked with Spamit.com
  13. ^ "Suspected 'Mariposa Botnet' creator arrested". .canada.com. accessdate=2010-07-30. {{cite web}}: Check date values in: |date= (help); Missing pipe in: |date= (help)
  14. ^ "Calculating the Size of the Downadup Outbreak — F-Secure Weblog : News from the Lab publisher=F-secure.com". 2009-01-16. Retrieved 2010-04-24. {{cite web}}: Missing pipe in: |title= (help)
  15. ^ America's 10 most wanted botnets
  16. ^ "Pushdo Botnet — New DDOS attacks on major web sites — Harry Waldron — IT Security". Msmvps.com. 2010-02-02. Retrieved 2010-07-30.
  17. ^ "Research: Small DIY botnets prevalent in enterprise networks". ZDNet. Retrieved 2010-07-30.
  18. ^ Warner, Gary (2010-12-02). "Oleg Nikolaenko, Mega-D Botmaster to Stand Trial". CyberCrime & Doing Time. Retrieved 2010-12-06.
  19. ^ "New Massive Botnet Twice the Size of Storm — Security/Perimeter". DarkReading. Retrieved 2010-07-30.
  20. ^ "Technology | Spam on rise after brief reprieve". BBC News. 2008-11-26. Retrieved 2010-04-24.
  21. ^ a b c d e http://www.messagelabs.com/mlireport/MLI_2010_04_Apr_FINAL_EN.pdf
  22. ^ Researchers hijack control of Torpig botnet - SC Magazine US
  23. ^ Chuck Miller (2008-07-25). "The Rustock botnet spams again". SC Magazine US. Retrieved 2010-07-30.
  24. ^ "Storm Worm network shrinks to about one-tenth of its former size". Tech.Blorge.Com. 2007-10-21. Retrieved 2010-07-30.
  25. ^ Spam Botnets to Watch in 2009 - Research - SecureWorks
  26. ^ http://www.theregister.co.uk/2010/03/16/waledac_takedown_success/
  27. ^ a b c d http://www.computerworld.com/s/article/9076278/Top_botnets_control_1M_hijacked_computers
  28. ^ http://www.theregister.co.uk/2008/05/14/asprox_attacks_websites/

External links

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