I don't know much about Authenitcated Users Group, but am curious - how did you delete it? Is it perhaps still sitting in your computer's recycle bin? If so, you should be able to easily restore it. I would also try attempting to go back to an earlier computer restore point if the recycle bin option does not work.
As for the potential computer infections, you should immediately install, update and run an antivirus program. Otherwsie, whatever progress you make in cleaning your computer will quickly get undone. If you are not familiar with the various brands of free antivirus programs, the best choice would be to simply download Microsoft Security Essentials directly from a Microsoft Corporatiion website. It is free and reportedly does a decent job. (Do not download it from non-MS websites, as there are also fake copies loaded with infections on other, non-MS websites)
You should also download, update and run the free version of SuperAntiSpyware (SAS) in Windows Safe Mode, plus do the same with MalwareBytes Antimalware (MBAM) in regular Windows mode. After running both of those programs, you might want to then post the resulting logs here at BleepingComputer, so the more expert advisors can look them over and advise you as how to proceed next.
Edited by Torvald, 09 September 2010 - 03:00 PM.