This is scumbag malware designed to take your machine hostage until you pay.
Here is the -quickest- way to eliminate this tediosity:
1. Register the scumware using this serial number: SL55J-T54YHJ61-YHG88
Once this is done it will allow you to now use your computer.
2. Open explorer and delete: C:Documents and SettingsAll UsersApplication Datadefender.exe
If the file is not there, search for: defender.exe and delete it.
3. Download SpyBot Search & Destroy and run it on your machine: http://www.safer-networking.org/en/download/