The virus is coming from a diskette.
Scan all the disks you were using at the time and clean(un-infect) them.
Once a diskette is uninfected remove it.
If you reboot with a virus in memory it will just write to the diskette.
If you put another diskette in the drive with a virus in memory it will write to it.
It is quite easy to spread a virus to many disks in a single session.
Those Australian Parasite Viruses are the worst, It is so hard to ship them back to NZ.. (Just joshing)