I have done this once before, but I only know how to do it on Vista.
Go to start and search for "rstrui" choose the one that pops up. Now chose another restore time when you didn't have security shield and click next. Now select a time and click next again. Now click complete and your computer will restore your old settings where you didn't have security shield. It might take some minutes.
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I personally have McAfee, and i did a bunch of research on this thin because i just got it myself. What I ended up doing (and it worked) was i restarted and entered "safe mode with networking" (get this option by repeatedly pressin f8 until the options for the safe modes appear).
I then ran McAfee and did a full scan (which took about 3 hours ) if you request to do the scan in the backround, you can still get online and do whatever.
I restarted again and let my computer load in the normal mode. My Security Shield was gone at this point, but I ran a full scan again just to be safe.