旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � VIRUS REPORT � � 1704 Format � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴� Synonyms: Blackjack, 1704, Falling Letters. Date of Origin: September, 1988. Place of Origin: Germany. Host Machine: PC compatibles. Host Files: Remains resident. Infects COM files. Increase in Size of Infected Files: 1704 bytes. Nature of Damage: Affects system run-time operation. Corrupts program or overlay files. Formats or erases all/part of the hard disk upon activation. Detected by: Scanv56+, F-Prot, IBM Scan, Pro -Scan. Removed by: CleanUp, M-1704, Scan/D, F-Prot. Derived from: 1701 (Cascade) virus. Scan Code: Uses self-encryption. FA 8B EC E8 00 00 5B 81 EB 31 01 2E F6 87 2A 01 01 74 0F 8D B7 4D 01 BC 85 06 31 34 31 24 46 4C 75 F8. The code for the 1704 virus is identical to the 1701 except for a single instruction. The only differences are the removal of a conditional jump from the 1701 (which would never have been taken), and some necessary segment overrides on the BIOS tests missing in the previous version. The virus was designed to not infect micros manufactured by IBM, but errors in coding enable it to infect any PC, regardless of origin. The virus tests the BIOS for the string "COPR. IBM", and contains code to not infect if it finds this - however there are errors in the code which prevent it from working. As with the 1701, the 1704 can recognize if it has previously infected a file. However, because recognition depends on the length of the virus, it will infect programs already infected by variants with different lengths. (1701 will infect COM files infected with 1704, and vice versa.) The encryption of this virus is different in each instance of the virus, being dependent on the size of the host file. The hard disk is formatted when the virus activates. This virus has been termed "Blackjack", which is a pun on the German name "17+4" of a popular card game. Blackjack infects only COM-files which are at least 3 bytes long, and it does so only once for any given file. It overwrites the first three bytes with a JMP to the beginning of the viral code, which is appended to the file. The 2 byte address of this JMP instruction is probably the reason why only COM files are susceptible to infection. Blackjack retains the file's time stamp. It even infects read-only files; on write-protected floppy disks, it attempts writing 5 times per file, thus revealing its activity. In the infected file, the viral code is cryptographically encoded, using a simple Vigenere code depending on the length of the file; only the instructions for decoding the encrypted part of the code are in plain machine-language. This is obviously intended as a impediment against disassembling. Hence, every copy of the virus looks different (depending on the length of the file). On invocation of an infected program, Blackjack installs itself in RAM (if no copy is already installed), then replaces the JMP instruction with its former contents and resumes normal program operation. The storage map shows that Blackjack has tinkered with the free storage pointer-chain to hide the fact that it has hooked interrupt 21. Hence, only a minor part of Blackjack is visible in the storage map. In every year, from October to December, Blackjack will interfere with CGA or EGA operated screens, moving randomly chosen characters down, like falling leaves in autumn. After a while, you'll have a big heap of characters at the bottom of your screen, and as you cannot see anymore what the computer is trying to display, you'll probably have to restart the system. This behaviour has been predicted by two people, who have disassembled Blackjack, and has later been observed on many EGA-equipped ATs. �袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴� � This document was adapted from the book "Computer Viruses", � � which is copyright and distributed by the National Computer � � Security Association. It contains information compiled from � � many sources. To the best of our knowledge, all information � � presented here is accurate. � � � � Please send any updates or corrections to the NCSA, Suite 309, � � 4401-A Connecticut Ave NW, Washington, DC 20008. Or call our BBS � � and upload the information: (202) 364-1304. Or call us voice at � � (202) 364-8252. This version was produced May 22, 1990. � � � � The NCSA is a non-profit organization dedicated to improving � � computer security. Membership in the association is just $45 per � � year. Copies of the book "Computer Viruses", which provides � � detailed information on over 145 viruses, can be obtained from � � the NCSA. Member price: $44; non-member price: $55. � � � � The document is copyright (c) 1990 NCSA. � � � � This document may be distributed in any format, providing � � this message is not removed or altered. � 훤袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴暠  Downloaded From P-80 International Information Systems 304-744-2253