It’s been a wild month for WordPress users; there has been a rash of WordPress sites getting hacked. If you haven’t checked your own site lately, you should. The symptom of the hack is that visitors to your site get redirected to a malicious site, typically ending in .ru (Russia). It’s pretty easy to test: go to your site :(.
You can also go to sucuri.net to do a free scan on your WordPress site.
The fix is complicated and different for each user. If you’re not technically-minded, get some professional help to clean out your site. Do a Google search for “WordPress site hacked” and go from there.