WordPress sites hacked

Several sites I have done show the following message when viewed in Chrome. Upgrading to 3.1 seems to fix it, but is there a plugin or something that can protect these sites from these kinds of attacks?

“Warning: Something’s Not Right Here!
websitename.com contains content from traffichistic.co.cc, a site known to distribute malware. Your computer might catch a virus if you visit this site.
Google has found malicious software may be installed onto your computer if you proceed. If you’ve visited this site in the past or you trust this site, it’s possible that it has just recently been compromised by a hacker. You should not proceed, and perhaps try again tomorrow or go somewhere else.
We have already notified traffichistic.co.cc that we found malware on the site. For more about the problems found on traffichistic.co.cc, visit the Google Safe Browsing diagnostic page.

If you understand that visiting this site may harm your computer, proceed anyway.”