Originally Posted by Ron Bennett

Flash ads is likely the culprit - they can run scripts and redirect. Flash can include all sorts of nasties.

I run Flashblock (technically it suppresses flash, doesn't truly block it; flash cookies are still set, which is intentional for Flashblock to work the way it does), which greatly speeds up browsing and, as an added benefit, makes browsing much safer.

For even more security, Noscript and similar add-ons are worthwhile, though can greatly limit usability of many sites unless one takes some effort to carefully, to ensure security is maintained, tweak various whitelisting and configuration settings.

Ron