There's a rogue security product out there that claims to be "Microsoft Security Essentials" but it has nothing to do with Microsoft. This malware/trojen is distributed via drive-by-download attacks as hotfix.exe or mstsc.exe

Microsoft Security Essentials is a free antimalware protection program from Microsoft, but a new malware threat identified by security software vendor F-Secure is also masquerading as Microsoft Security Essentials.

The "alert" from the threat steals the Microsoft Security Essentials brand, including the little blue fortified castle icon. This alert titled as Microsoft Security Essentials Alert and states that a Trojan was detected on your computer. It will list this Trojan as Unknown Win32/Trojan. It will then prompt you to clean your computer. See the screenshot below :

Beware : Fake Microsoft Security Essentials Rogue
When you click on the Clean Computer or Apply actions button, it will state that it was unable to remove it and then prompt you to scan online. If you click on the Scan Online button it will list 35 different anti-virus programs, 30 of which are legitimate anti-virus programs and 5 that are rogues that the Trojan is distributing. These five are AntiSpySafeguard, Major Defense Kit, Peak Protection, Pest Detector and Red Cross. These all are fake anti-virus programs.