Security essentials 2011 is a fake security software (rogue). It replaces Security essentials 2010, Internet Security 2010 and Advanced Virus Remover.
Security essentials 2011 displays a lot of warning messages, change the desktop background, detects fake infections and blocks softwares execution. It comes from fake online scanners, malicious porn sites, fake cracks and exploits.
If your PC is infected with Security essentials 2011, use MBAM to remove the infection.