F-Secure Virus Descriptions : Ufa

Ufa is a direct action file virus which tries to infect several COM files every time when an infected program is executed.

It seems that the virus author has tried to make the virus to overwrite a random sector on the current drive with garbage, if the virus has been in the system for 30 days. However, the virus code contains a bug which usually prevents this.

Virus searches candidate files to be infected in the current directory and then up to 9 directories along the search path. Virus attempts to infect a maximum of 10 files in each directory. Because this might take a long time, especially on slow computer, virus has a time limit for infection. When the limit has been reached, virus stops infecting files. Next time, when an infected program is executed, virus starts infecting files again. During the infection process, virus disables the Ctrl-Break key sequence.

If files match "*.COM", have the archive bit set and are not system or hidden files, they are checked for infectability. Files smaller than 512 bytes are not infected. The virus does not reinfect infected files. Virus can't preserve the file date, so all infected files has their date and time fields changed to the moment infection took place.

This virus seems to be written in BASIC or some similar high-level language.