- You may be looking for Y2K bug.
The Millennium Bug was a name jokingly given by Alex Hopkins to an alien he sent Jack Harkness after New Year's Eve 1999. It had eighteen legs and was filled with poison. Hopkins sent Harkness after the creature to distract him from his plans to kill the rest of the Torchwood Three team. Alex accomplished this task before Jack returned and then committed suicide, leaving Harkness in charge of the branch. (TV: Fragments)