Hi All
as usual, after some period, there is another large bunch of Trojan-gens added in the today’s update. We have tested is for long time so I do not expect serious problems from it. If you have some file which you believe is not Trojan-gen however, please send it as soon as possible to virus [at] avast [dot] com e-mail address.
Thank you for your cooperation 
!!
Pavel
Hello sir,
I would like to ask you something:
What is this trojan - gen? A trojan found with heuristics or something?
I searched in Vgrep about the name of this virus in other companies, but it returns so much different viruses that I get lost… Trojan - Gen represents more than one trojan for other companies?
Thanks,
Elminster
Gen is short for generic
Hello Elminster and Eddie,
This is a very good basic explanation how Virus Scanning works.
http://cse.stanford.edu/class/cs201/projects-00-01/viruses/anti-virus.html
There are also virus scanning applications that work without signature scanning, all files that are trusted are excluded and all other files are considered untrusted, and possibly malicious. Principal antivirus and InVircible are such programs, but you must know your system to a jiffy to profit from these programs (admins).
polonus
P.S This is also a good info base:
http://www.cknow.com/pages/Virus-Tutorial