Gen stands for generic no name Trojan
You need to run these 5 essential steps to remove all the Trojan on your computer.
1. Run Deckard's System Scanner (DSS)
2. Run Malwarebytes Anti-Malware
3. Run the anti spyware removal programs spybot
4 Run Superantispyware
5. Run a complete scan with free curing utility Dr.Web CureIt!
2nd answer:
The first answer doesn't really tell what Trojan.gen is. Trojan.gen is a computer virus that slows down your computer(a lot), collecting your personal information without you knowing, damaging your computer system, and deletes files without your consent.