Avast not detecting a virus

I have a virus which puts a csrss.exe file in the c:/windows folder (not the correct place) and it gets blocked by the windows anti spyware program as a trojan. When deleted it returns (i have turned off system restore) but avast does not pick up the virus. What can I do ? is there a way to submit files to avast for analysis ?

Sure - send the file to virus@avast.com, with a short explanation (something like what you wrote here).
Thanks.