Gremlins
This nasty little classic is a disguised daemon that interrupts CPU processing with random program requests. It also reproduces itself, wiping similarly sized programs on the target system while it does so. It's not very subtle, and sysops soon notice the problem and purge these pests, but until the purge, Gremlins eat programs, and any program running on the target system has a 1 in 6 chance of crashing when encountered—this does include file servers and other programs a 'runner might want to run! Gremlins are indiscriminate.
Options: Pseudo-intellect, Movement, Recognition