Computer virus

Computer viruses are software programs infecting computers for various usually malicious reasons. The Doctor gave Mickey Smith a computer virus that would erase all evidence of his existence from the Internet. (DW: World War Three). Given that Elton Pope was able to access information on the Doctor online a year later, it is probable that the virus the Doctor gave Mickey was never used.

A Bad Wolf virus had at some point erased all info on Rose Tyler from the Torchwood database. (DW: Love & Monsters)

Cyberterrorists developed the Armageddon virus to bring down the international banking network, and the virus was later used by Alan Jackson to reprogram Mr Smith. (SJA: The Lost Boy)

The Movellans were slaves before they were freed by a computer virus. (FASA's The Doctor Who Role Playing Game)

A computer virus was made by the Doctor on a mobile phone that reverted all computers and networks to display only the number zero, to alert the Atraxi of Prisoner Zero's presence.