TrustDoctor aka Trust Doctor is a fake anti-virus from the WiniSoft family of rogueware. The trial version of TrustDoctor may enter a system via fake codec downloads or drive-by downloads. Once TrustDoctor is inside a system it will create harmless files which will later be detected as malware when a fake system is conducted.
TrustDoctor will also display random security alerts and pop-up warning messages in order to scare a user into purchasing its "full" version as a remedy. Whatever you do, make sure you do not waste your money on this useless application; TrustDoctor is not to be trusted and should be removed upon detection.