Don't know the technical background if the same engine is still used. But I guess so, just updated definition files.
Anyway, Microsoft Antispyware is indeed renamed to Windows Defender. Maybe because it does indeed likes to remove random applications instead of just removing spyware. Or maybe they renamed it to Windows Defender because it defends Windows' by allowing Remote Desktop while any VNC server is very evil. Or maybe they just renamed it because of the bad name in general they were building up. God knows.
Remember:
This is the same software that thinks Symantec (Norton) Antivirus is a password stealing virus and corrupts Norton because of that so your precious system will not be protected anymore against viruses at all.
/ 
