CIH (computer virus)
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CIH, also known as Chernobyl or Spacefiller, is a Microsoft Windows 9x computer virus which first emerged in 1998. It is one of the most damaging viruses, overwriting critical information on infected system drives, and more importantly, in most cases overwriting the system BIOS. The virus was created by Chen Ing-hau (陳盈豪, pinyin: Chén Yíngháo) who was a student at Tatung University in Taiwan. 60 million computers were believed to be infected by the virus internationally, resulting in an estimated $1 billion US dollars in commercial damages.
Chen claimed to have written the virus as a challenge against bold claims of antiviral efficiency by antivirus software developers. Chen stated that after the virus was spread across Tatung University by classmates, he apologized to the school and made an antivirus program available for public download; the antivirus program was co-authored with Weng Shi-hao (翁世豪), a student at Tamkang University. Prosecutors in Taiwan could not charge Chen at the time because no victims came forward with a lawsuit. These events led to new computer crime legislation in Taiwan.
The name "Chernobyl Virus" was coined some time after the virus was already well known as CIH, and refers to the complete coincidence of the payload trigger date in some variants of the virus (actually the virus creation date in 1998, to trigger exactly a year later) and the Chernobyl accident, which happened in the Ukrainian SSR on April 26, 1986.
The name "Spacefiller" was introduced because most viruses write their code to the end of the infected file, however CIH looks for gaps in the existing program code where it writes its own code. This does not increase the file size and in that way helps the virus avoid detection.
In September 1998, Yamaha shipped a firmware update to their CD-R400 drives that was infected with the virus. In October 1998, a demo version of the Activision game SiN was infected by one of its mirror sites. In March 1999, several thousand IBM Aptivas shipped with the CIH virus, just one month before the virus would trigger.
CIH's dual payload was delivered for the first time on April 26, 1999, with most of the damage occurring in Asia. CIH filled the first 1024 KB of the host's boot drive with zeros and then attacked certain types of BIOS. Both of these payloads served to render the host computer inoperable, and for most ordinary users the virus essentially destroyed the PC. Technically, however, it was possible to replace the BIOS chip, and methods for recovering hard disk data emerged later.
The virus made another comeback in 2001 when a variant of the LoveLetter Worm in a VBS file that contained a dropper routine for the CIH virus was circulated around the internet, under the guise of a nude picture of Jennifer Lopez.
A modified version of the virus called CIH.1106 was discovered in December 2002, but it is not considered a serious threat.
CIH spreads under the Portable Executable file format under Windows 95, 98, and ME. CIH does not spread under Windows NT-based operating systems, such as Windows 2000, Windows XP, Windows Vista, Windows 7, Windows 8, and Windows 8.1.
CIH infects Portable Executable files by splitting the bulk of its code into small slivers inserted into the inter-section gaps commonly seen in PE files, and writing a small re-assembly routine and table of its own code segments' locations into unused space in the tail of the PE header. This earned CIH another name, "Spacefiller". The size of the virus is around 1 kilobyte, but due to its novel multiple-cavity infection method, infected files do not grow at all. It uses methods of jumping from processor ring 3 to 0 to hook system calls.
The payload, which is considered extremely dangerous, first involves the virus overwriting the first megabyte (1024KB) of the hard drive with zeroes, beginning at sector 0. This deletes the contents of the partition table, and may cause the machine to hang or cue the blue screen of death.
The second payload tries to write to the Flash BIOS. Due to what may be an unintended feature of this code, BIOSes that can be successfully written to by the virus have critical boot-time code replaced with junk. This routine only works on some machines. Much emphasis has been put on machines with motherboards based on the Intel 430TX chipset, but by far the most important variable in CIH's success in writing to a machine's BIOS is the type of Flash ROM chip in the machine. Different Flash ROM chips (or chip families) have different write-enable routines specific to those chips. CIH makes no attempt to test for the Flash ROM type in its victim machines, and has only one write-enable sequence.
For the first payload, any information that the virus has overwritten with zeros is lost. If the first partition is FAT32, and over about one gigabyte, all that will get overwritten is the MBR, the partition table, the boot sector of the first partition and the first copy of the FAT of the first partition. The MBR and boot sector can simply be replaced with copies of the standard versions, the partition table can be rebuilt by scanning over the entire drive and the first copy of the FAT can be restored from the second copy. This means a complete recovery with no loss of user data can be performed automatically by a tool like Fix CIH.
If the first partition is not FAT32 or is smaller than 1GB the bulk of user data on that partition will still be intact but without the root directory and FAT it will be difficult to find it especially if there is significant fragmentation.
If the second payload executes successfully, the computer will not start at all. A technician is required to reprogram or replace the Flash BIOS chip, as most systems that CIH can affect predate BIOS restoration features.
This variant is the most common one and activates on April 26.
It contains the string: CIH v1.2 TTIT
CIH v1.3/CIH.1010A and CIH1010.B
This variant also activates on April 26. It contains the string: CIH v1.3 TTIT
This variant act on the 26th of any month. It is still in the wild, although it is not that common. It contains the string CIH v1.4 TATUNG.
This variant activates on August 2 instead of April 26.