Trojan.Win32.BlackBird (also know as Worm.Win32 or BlackBird) used to be a real virus, now fake anti-spyware software like IE Defender will display Trojan.Win32.BlackBird as their scan result to trick user to buy the fake anti-spyware program. The fake anti-spyware program usually get installed onto your PC without your permission, through Trojan, malware and virus (or [...]

Source: http://www.xp-vista.com/spyware-removal/trojanwin32blackbird-blackbird-removal-instructions