I had the same thing happen a month or two ago. It was called prolivation hijacker. Here's an article that I used to get rid of it..
What is Prolivation.com?
Prolivation.com takes over your ability to view webpages by attaching the URL
prolivation.com/cgi-bin/r.cgi?
in front of any web page you try to visit. In essence, this destroys the ability to view web pages since currently the domain prolivation.com is actively registered but dormant. The script itself allows the site to monitor visited URLs and/or redirect the requests, add popups, etc. Adult sites may be substituted for the requested site.
How does Prolivation.com hijack my homepage?
The hijacker edits the registry as well as editing the file to reset the home and search pages for Internet Explorer. Because of these changes to your system the hijacker program is difficult to remove.
How to I Remove Prolivation.com?
Follow these instructions to manually remove the prolivation.com hijacker from your system.
• Click on Start, Run
• Type in REGEDIT and press Enter
• In the left column, click the plus signs (+) next the the following items
HKEY_LOCAL_MACHINE
SOFTWARE
MICROSOFT
WINDOWS
CURRENTVERSION
URL
• Click on the Default Prefix folder
• In the Right Pane, double-click on (DEFAULT) in the name column, and change the value to
http:// and click OK
• Now in the Left Pane, click on Prefixes
• In the Right Pane, double-click on FTP in the name column and change the value to
ftp:// and click OK
• Double-click on GOPHER in the name column and change the value to
gopher:// and click OK
• Double-click on HOME in the name column and change the value to
http:// and click OK
• Double-click on MOSAIC in the name column and change the value to
http:// and click OK
• Double-click on WWW in the name column and change the value to
http:// and click OK
• Close REGEDIT
Because this hijacker may change the default home and search page URLs, its also wise to check the following file for changes.
• Open My Computer, and click on Tools
• Click on Folder Options
• Click on the View tab
• Make sure "Show Hidden Files and Folders" is dotted and "Hide extensions for known file types" is unchecked
• Click on Ok
• Double-click on Drive C in My Computer
• Double-click on Windows (or WINNT for NT/W2K/XP)
• Double-click on the INF folder
• Right-click on IERESET.INF, and OPenis EnlargementN WITH Notepad.exe
• Find the [Strings] and make sure it does not contain "prolivation.com"
• If it is set to "prolivation.com" change the start_page_url and search_page_url values.
• For IE 6, this would be:
START_PAGE_URL="http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome"
SEARCH_PAGE_URL="http://www.microsoft.com/isapi/redir.dll?prd=ie&ar=iesearch"
• Save the file