Gift.553
Description Gift.553
These are not dangerous memory resident parasitic viruses. "Gift.724" is encrypted. They hook INT 21h and write themselves to the beginning of COM files that are searched. While installing memory resident the viruses allocate a 64Kb block of DOS memory that may decrease the system performance.
The most interesting feature of these viruses is their structure: it follows the standard ZIP archives binary format. The beginning of virus code is very similar to ZIP header, and to the end of infected files a block of data is written that is similar to ZIP "end-of-archive" data. Despite on this, when infected files are run, these data are executed as a sequence of legal assembler instructions that pass control to the main virus code. As a result, the infected files can be not only executed as DOS programs, but also can be accessed as ZIP archives. These "archives" contains just one file named "SMF_Gift.com". Being "extracted" this file is the same as original contents of infected file.
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Ai22.1659
Description Ai22.1659
It is a harmless memory resident parasitic virus. It installs itself memory resident and replicates only under DOS 5.x and 6.x. It hooks INT 21h and writes itself to the end of .COM and .EXE files that are executed. While installing the virus also infects the C:COMMAND.COM file. The virus does not manifest itself in any way, it contains the ID-text:
Ai22
Aids.552
Description Aids.552
It is a very dangerous memory resident parasitic virus. It hooks INT 3, 21h and writes itself to the end of .EXE files that are closed.
This infector writes a part of its code into each 16th .COM file that is closed. These files cannot be recovered because the original information is not saved. When such file is executed the virus displays "AIDS" in large letters (graphic video mode).
Aids.872
It is a harmless nonmemory resident parasitic virus. It searches for .COM files and writes itself to the end of the file. It contains the text string:
Aids
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