Trainers are memory resident programs that alter the behaviour of a game. Your anti-virus software may detect them as malware (viruses, worms, trojans, bots etc.). This is almost always a false alarm.
If you get a warning message by Google or Firefox, please ignore it. They (Googlebot) mistakenly think that some files on our Trainers section are "malicious content" and have decided to randomly display warning messages when downloading files.