Stuxnet is a virus which affects PLC.
Stuxnet worm was discovered attacking Siemens PCS7,S7 PLC and WIN-CC system around the world.
Infected 100000 computers and at least 22 industrial sites.
Created to destroy uranium enrichment centrifuges in iran.
The worm reprograms Siemens 315 PLC’s to sabotage frequency converted speeds.This causes the centrifuges rotor to revolve at the incorrect speed for normal operation.The abnormal frequency changes may eventually cause physical damage to the centrifuge.
Watch the video - It will show how stuxnet infects a PLC.