If you had Security Center pop up and it was trying to sell itself, then that is the security center virus/bug/whatever and not actually Microsoft. So that is not legit.
Ive had this before and it does suck but not that hard to clean.
If your not willing to pay for protection like Norton, I ran the cheapest net version of Norton for a year and it worked great. U dont need the large suite packages. I Find a compilation of the following free products works the best. Always run this stuff in safe mode so bad things don't get loaded. Once you feel your system is clean, run everything once more for safeties sake in safe mode and then run again in normal mode.
Malware Bytes Anti-Malware
Search and Destroy
The real Microsoft Security Center Windows Defender.
CCleaner
If you do safe mode with networking, make sure to physically remove your Ethernet wire from your computer or disconnect your wireless so you aren't connected to the net and things cant re-download. Also make sure to check in the control panel in internet options/connections tab/LAN settings to make sure a proxy has not been added. Under proxy setting, field should be blank and box should be unchecked, that is of course if you are not set up to go through a proxy on purpose.
Ive only had to do a fresh install on a computer twice due to virus once on a cpu of mine and once on a clients. fresh installs should be last ditch effort IMO, only because i hate having to re-install everything. Sometimes its just better to spend a day cleaning the infected computer.
All good suggestions for sure..
The combination I use is about the same.
Microsoft Security Essentials (Free, and replaced Defender)
CCLEANER (Free and cleans sludge and registry errors)
Spybot Search & Destroy (Free, and cleans ad ware)
Malware Bytes (Free and cleans most infections
if caught early)
Threatfire (Free, and detects rootkits)
Another option is Avast. I love the way Avast stops drive by downloads.
When or if a website tries to download crud, Avast breaks the connection, and stops it in its tracks. Very good stuff.. (If you use this one, MSE is not needed)
Just my humble opinion..
As to the XP2009 (or 2010, 2011) virus, disguised as an anti virus, it's difficult to remove, save some time and format and install the OS again.
Quit screwing around and format..