Udate: 10-5-2010: While RemoveVirus.org has been unable to locate this virus to write a removal guide OUR community has responded and written many solutions below.
Description: Antivirus IS is related to Antivirus Soft, Security Suite and AV Security Suite. Because this threat acts in the exact same manner we are not going to create a dedicated guide to removing this threat. You can simply follow the above links to those removal guides and see the exact steps that need to be taken. We do want to point out that those guides also contain videos that help describe steps to remove this threat.
If you have specific questions please ask them below in the comments section. It looks like the community has already found a solution. Read the comments.
However we are still working on a manual removal guide for Antivirus IS. We need your help in finding the virus. If you know what site you got infected on please post the URL for us to download the fake client. Normaly we have access to new threats but not this one.
As of 10-3-2010 We can not confirm any security client works to remove this threat. However there are comments bellow to suggest otherwise.
ABSOLUTE WORST CASE FOR YOU: I normaly hate to recommend out products and services for viruses we have been unable to disect. However http://www.pcninja.com remove this threat for you as well as all other viruses. It does cost $99.99 but they are true experts at removing viruses.

My name is Jacob and I run the RemoveVirus.org website with several other pros. Our virus removal guides are the most indepth guides around and provide real solutions. If you purchase an Antivirus Client we endorse on this site from one of the links we do make a commision. This helps us run and maintain the virus removal website. To date we have helped ten's of thousands if not hundreds of thousands of people remove their virus threats.
