Pinged, but Request timed out

C:\>ping www.google.com

Pinging www.l.google.com [64.233.179.99] with 32 bytes of data:

Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 64.233.179.99:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Then I pinged www.yahoo.com, there is no problem.

I am wondering if some kind of trojan caused problem. If so, what kind of anti-virus program can kill trojan?