These are very dangerous memory resident parasitic viruses. They hook INT 10, 21h and overwrite KEYBGR.COM (if it exists in the current directory) while executing any program. Depending on their counters these viruses manifest themselves with a noise (by PC speaker). The viruses contain the text strings:
This program is a VIRUS program.
Once activated it has control over alls
ystem devices and even over all storage
media inserted by the user. It continually
copies itself into uninfected operating
systems and thus spreads uncontrolled.
The fact that the virus does not destroy any
user programs or erase the disk is merely due
to a philanthropic trait of the authorall...
