Links to WP site redirecting to malware site

We’re running WP 2.9.2, just upgraded yesterday. Now it appears we have been hacked.

From some external sites, links to our WP site redirect to a malware site [link to malware site removed]. This doesn’t happen when typing in our WP URL directly, nor from all external sites, but once it happens from a site, it happens repeatedly.

I can’t find any redirect commands in our installation (eg in .htaccess), but I’m not a web expert. I’m reluctant to post our URL, but here is a screen shot of HttpFox header information from one of the redirect events:

https://www.flickr.com/photos/37343108@N02/4391602094/sizes/l/