I just got hit by this:
http://www.spywarevoid.com/remove-security-shield-2011-securityshield2011-removal-guide.html
similar to system check. when in normal mode it would not allow me to open any specialty anti-virus or spyware programs, including malmarebytes (sp). microsoft security esentials could not locate the program (it let it in, so not a suprise). the program also would not allow me to open any web browsers.
Ended up rebooting into safe mode with networking enabled. Malwarebytes was able to run, but could not find anything (probably because security shield was not loaded). ended up doing a system restore to 3 days prior. Problem solved....for now.