Hi Guys,

Well as the title says I need some help with a virus problem.  I'm currently helping a Veterans group that provides services to Vets.  One of 3 PCs is infected.  It runs XP SP2.  It has McAfee (Comcast provided),  Spybot Search and Destroy, and Malwarebytes Antimalware (free version) installed.  I have scanned with all three.  They have removed some Viruses (trojans) but now they come up blank.  I'm using Tea-timer on it and have Immunized IE8 to block harmful websites.

The symptoms.   1). When running IE8 a new IE8 window will automatically open attempting to contact a blocked website.  This results in 505 error.  (Reminds me of a trojan) 2). When doing a search in Yahoo, Google or Bing the search results are corrupt.  Clicking on any links results in random web pages being connected but, always harmless web pages. (Reminds me of a Bot). 

I'm looking for safe effective advice for ridding this machine once and for all of all bots and trojans.

Help!!!!