I purchased a new Dell in 6/2008 with Vista and Windows PC Defender was already installed on the computer.  Now I am receiving a lot of pop ups from Windows PC Defender stating that I have several trojans, etc. and to click a button to protect.  When I click the button I am sent to Windows Defender to purchase and / or to activate.  Is this legitimate?  I have McAfee installed and these trojans are not showing up on the scan.  So if someone could help me I would appreciate it.