We will need more information to be able to help you:
- Which OS are you using? Is it up to date?
- What avast! version and VPS file (virus database) number?
- Like David asked, what was the filename and path where the virus was found?
- Which actions have you taken to try solving the problem?
- Do you use a firewall? Which one?
- Do you have any other antivirus installed in your system? Had in the past?