We've recently become aware of malicious websites that exploit a vulnerability in unpatched versions of Internet Explorer. If your system is unpatched and you happen to visit one of these "booby-trapped" websites, you may find that your web browser has been hijacked.
When your web browser is hijacked, attempts to view some websites (such as common search engines or popular web directory sites) get automatically redirected to an alternative website of the hijacker's choice without your consent, frequently via a BHO (Browser Help Object). Because it is common for alternative sites to feature explicit adult content, this can obviously be a rather disconcerting experience.
The modifications made by the browser hijacking code may result in system stability issues or general system performance slowdowns, the browser hijacking code may compromise your privacy or the security of what you do online by "reporting back" to its controllers on the sites you visit, or information you pass to those sites, your desktop may begin displaying pop-up advertisements, and the browser hijacking code may contain features designed to actively resist removal of the infestation using standard anti-spyware or anti-virus programs.
If your browser is definitely being hijacked (e.g., you attempt to go to Google but get sent to some other site instead), your first step should be to run Norton Anti Virus, Panda Software or MacAfee. Your second step should be to run Spybot Search and Destroy and/or Ad-aware. Our experience has been that they will flag and remove at least some spy ware software that Norton or some of the others doesn't catch.