trojan.agent/gen-nullo [Short]

Did a full scan with Superantispyware on thursday night and it picked out 2 versions of this ,
Did a full scan with avast Free this morning and it picked out nothing .
Now using SAS again fully and its picked out only 1 trojan.
How come Avast didnt picked it up this morning and how do i get rid of it ?

Any help would be appreciated

thanks .

With no information to work with no one can answer your question.

If you can post the full information from the SAS Log (View Scan Logs), file name and location of detection, etc. ?