EICAR test file
The EICAR Anti-Virus Test File or EICAR test file is a computer file that was developed by the European Institute for Computer Antivirus Research (EICAR) and Computer Antivirus Research Organization (CARO), to test the response of computer antivirus (AV) programs. Instead of using real malware, which could cause real damage, this test file allows people to test anti-virus software without having to use a real computer virus.
Anti-virus programmers set the EICAR string as a verified virus, similar to other identified signatures. A compliant virus scanner, when detecting the file, will respond in more or less the same manner as if it found a harmful virus. Not all virus scanners are compliant, and may not detect the file even when they are correctly configured. Neither the way in which the file is detected nor the wording with which it is flagged are standardized, and may differ from the way in which real malware is flagged, but should prevent it from executing as long as it meets the strict specification set by European Institute for Computer Antivirus Research.
The use of the EICAR test string can be more versatile than straightforward detection: a file containing the EICAR test string can be compressed or archived, and then the antivirus software can be run to see whether it can detect the test string in the compressed file. Many of the AMTSO Feature Settings Checks are based on the EICAR test string.
The developers of one anti-virus software, Malwarebytes, have said that they did not add the EICAR test file to their database, because "adding fake malware and test files like EICAR to the database takes time away from malware research, and proves nothing in the long run." 
The file is a text file of between 68 and 128 bytes that is a legitimate executable file called a COM file that can be run by MS-DOS, some work-alikes, and its successors OS/2 and Windows (except for 64-bit due to 16-bit limitations). When executed, the EICAR test file will print "EICAR-STANDARD-ANTIVIRUS-TEST-FILE!" and then will stop. The test string was written by noted anti-virus researchers Padgett Peterson and Paul Ducklin and engineered to consist of ASCII human-readable characters, easily created using a standard computer keyboard. It makes use of self-modifying code to work around technical issues that this constraint imposes on the execution of the test string.
NOTE: The third character is the capital letter 'O', not the digit zero.
(Hashed with trailing newline character)
- Official Site of the European Institute For Computer Antivirus Research (also known as the European Expert Group for IT-Security)
-  Assembly-language analysis of the EICAR test file
-  Antivirus results from scanning the EICAR file
- "The Use and Misuse of Test Files in Anti-Malware Testing". Anti-Malware Testing Standards Organization. Archived from the original on August 16, 2017.
- "Is Your Antivirus Working?". PCMAG. Retrieved 2017-04-17.
- "How To: Test the SmartScreen Filter and Windows Defender Detection Scenarios". winsupersite.com. Retrieved 2017-04-17.
- Hess, Ken. "360 Total Security Anti-virus first impressions: Refreshingly subtle but thorough | ZDNet". ZDNet. Retrieved 2017-04-17.
- AMTSO guidelines on use and misuse of test files
- Malwarebytes developers on EICAR test file
- Why doesn’t Malwarebytes detect EICAR?
- Eddy Willems, “The Winds of Change: Updates to the EICAR Test File”, Virus Bulletin June 2003
- "EICAR test file | Virus Profile & Definition | McAfee Inc". home.mcafee.com. Retrieved 2017-04-17.