Some Common PC-DOS Viruses and What They Mean To You1.7 The 17xx VirusesThe name "17xx" refers to a family of viruses, sometimes called (among other things) Cascade, Blackjack, or Falling Tears. The most common members of this family are the 1701 and 1704 viruses. Like the 1813 and Sunday viruses, the 17xx viruses load into memory when the first infected program is executed, and remain resident until power off or reboot, infecting files which are executed. Unlike those viruses, the 17xx viruses infect only COM-format files (2) The virus will also occasionally cause all the letters on the display to fall into a "heap" at the bottom of the screen; this happens only very rarely if the year is after 1988, however.
1.7.1 SpreadExcept for the fact that only COM-format files are infected, the 17xx viruses spread through the same channels as the 1813 and Sunday.
1.7.2 SymptomsAs usual, the most reliable symptom of infection with the 1701 or 1704 virus is an alert from an anti-virus program. The "falling letters" effect happens only if the system date is in October, November, or December of 1988, or if the date is January 1st 1980 when the virus first loads, and is later set to a date after October 1988. So many systems may be infected with the virus for long periods of time without the display appearing. Infected files will grow by 1701 bytes or 1704 bytes (depending on the exact strain of the virus), but the typical user will not notice that.
1.7.3 DamageThe most common members of this family do no intentional damage at all, and if the virus is detected early the only cleanup involved will be erasing the infected files and replacing them with good copies. One rare member of the family (the "1704-Format" virus) will attempt to format part of the hard disk when it activates; recovering from that activation requires restoring the disk from backups.
1.7.4 ProtectionLike most of the commonest viruses, the 1701 and 1704 are old and well-known. They are also simple to detect, and any good anti-virus program should be able to detect or prevent them.Footnotes: (2) COM-format files usually have the extension "COM", although overlay files in COM format may have any extension at all, and a few files with extension "EXE" are actually in COM format. The details are unimportant; a good anti-virus program will do the right thing. [ Top of Page | Previous Page | Next Page | Table of Contents ] |