hello, all,
I need a great free software of anti-virus, who can advise me ,thank you

Doesn't exist. The only free one I know of (ClamAV) is damn near useless.

Just shell out the cash and pay for Kaspersky, Symantec, or McAfee.

Oh, and BTW, this thread should really be in Off-Topic.

well i dont know if these are great or not but sure are free

http://free.grisoft.com/doc/1
http://www.avast.com/eng/avast_4_home.html
http://www.free-av.com/
http://www.clamwin.com/

Usually free version from commercial AV does not contain "real time protection", I don't know if it is important for the system security, it is for the computer resources I believe. Anyway you can also make sure you're not infected by using online scans, they don't remove malwares though. Being owned is not worse than not knowing it.

"The best things in life are free" axiom does not apply to software.

Try leeching McAfee Enterprise edition off the net. Its the best.

Avast! home version does include on-access scanning.