There are 3 variants:
When the virus is run, it overwrites a DOS executable by random, but not every time, it might have to run a number of times in order to infect one file.
Files infected by the virus will no longer function properly but spreading the virus.
Skism.554 and Skism.x Edit
These variants do not manifest themselves.
When an infected program is run on Friday 25th, the virus displays an ASCII picture with these messages:
The man who brought you 622, Skism One, Caption Trips, and Sub-Zero now shanks you again, with his latest... Skism 1992 - Virus!!!! Get a late pass!
And it hangs the system.
If COMMAND.COM has been infected by the virus, every time the system boots up on this day would result on displaying this screen.