There is an excellent removal guide here: http://www.bleepingcomputer.com/virus-removal/remove-my-security-shield which I obtained through a Google search.
BleepingComputer is a very reliable source.
Scroll down that page as the first links you see are all advertising, so don't click the first thing you see, read it all first.
Moved this to Malware Discussion > Home User Assistance.
Yes this is a Great site.Be sure that if you have to run the Rkill tool.If it does not take right away to try it again.I have read up on this tool from the Author and there have been instances were you have to run numerous times. Occasionally it will not kill the running malware as some malware recognizes rkill and tries to protect itself.
I always tell the users the same thing and cant ever get tired of stressing upon it.
Please use these 2 excellent freebies out there :- 1} Malwarebytes Antimalware and 2} Superantispyware.
Use them as On demand scanners. The Security Shield virus that has infected your machine can easily be removed using the Bleeping computer link that Peter gave you in one of the posts here.
Also, it is a good idea to keep the two freebies that I mentioned above installed and up to date on computer and jsut scanning your computer once a week on demand. NO ANTIVIRUS can guarantee complete protection for any one.
Please revert if you were able to successfully remove the malware. Rest assured Security shield can be removed. It is nasty but trust me, its not the worst I have seen