If it keeps appearing, you have more than one, avast will alert for a virus detection and waits for the user to decide the action to take, it will then continue with the scan and if it finds another it will alert again.
What were you doing when avast alarmed ?
What avast! version and VPS file (virus database) number, e.g. 0436-4 (see about avast!)?
What was the virus name, what was the filename, where was it found
example (C:\windows\system32\infected-filename.xxx)?
What actions have you taken to try and resolve the problem?
Do you have a firewall, if so what ?