windows - How to make sure a system is not infected by a specific trojan?

In this case it's the TR/Alureon.19456U.3 trojan. On this Antivir site it's stated to be detected:

http://www.avira.com/en/threats/section/vdfhistory/ivdf_no/7.01.05.243/7.01.05.243.html

The system in question doesn't have the symptoms (lags, Firefox crashed) either.

Is there a way to be sure the trojan is not active?