There's an ongoing cleanup being recorded at BleepingComputer : the link is at
If you read through the posts made so far you'll get an idea of what DoSearches does and doesn't do when it's installed. The question of how it gets on to a system is not addressed but my bet is that it comes bundled with a download - possibly a game.
The main cause of DoSearches.com being active in all browsers is that it modifies the browser links. I can't see much sign of it being a serious threat (major registry modifications, modifying the MBR) - not yet, anyway.
From the thread the two most useful repair tools seem to be Shortcut Cleaner
and AdwCleaner (http://www.bleepingcomputer.com/download/adwcleaner/)
I suggest you try those two and follow up with a Malwarebytes full scan.
With apologies to Marius at BleepingComputer, who has been painstakingly guiding another user through the cleanup operation for the past week, for cherry-picking the bits that seem most likely to achieve a result.
You may remove this Do Searches virus (browser hijacker) for free if you follow this guide - http://www.system-tips.net/remove-dosearches-com-browser/
But! Don't buy this program described there. You don't need to. Simply install it and then click "Tools" and "Reset browser settings". This is a free utility to remove browser hijackers.