Redirecting to a malicious site

Perhaps your hosts file is hacked. Windows checks the Hosts file before it queries any DNS servers, which enables it to override addresses in the DNS.
Your hosts file is most likely located in C:\Windows\System32\drivers\etc, but check the registry for the exact location:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\DataBasePath

See this link for more information: http://winhelp2002.mvps.org/hosts.htm[^]

It could be a browser Helper Object. Some anti-viruses don't count those. You can try and disable all of them.
Allot of free games like to slide tuff in with the downloads because people rarely check the Eula. Some of them have a checkbox in them not to install the addon.They are checked by default to install.
If the antiviruses are not finding it they may not have the signatures for it yet.

You can use a program called Autoruns to see what is auto starting in the background. Located here: http://technet.microsoft.com/en-us/sysinternals/bb545021[^]

Also running process monitor form the same site can give an idea of extra stuff that shouldn't be there. (Bigger version of task manager

Also once you download the tools you need Disconnect from the internet so the bad files can't call home and re-infect.

Then when clean reconnect.