Microsoft Security Essentials 4.0 (free) released so quietly that I almost missed it. In truth, Microsoft doesn't refer to the version number at all, just to "the latest version of Microsoft Security Essentials." There isn't a lot that's new here, and my test results were about the same as before, so perhaps downplaying the new version makes sense.
Saved by Windows Defender Offline
Microsoft Security Essentials installed successfully on ten of my twelve malware-infested test systems. Ransomware on one test system made launching normal Windows impossible, and Microsoft Security Essentials won't install in Safe Mode. On the advice of Microsoft Tech Support I downloaded the bootable Windows Defender Offline. A full scan with this tool solved the problem and allowed me to complete the installation.
On another test system, Microsoft Security Essentials refused to update or scan because it claimed the system was not running a valid copy of Windows. In truth, the Windows installation was fine, but malware fooled the antivirus into thinking otherwise. Tech support advised reinstalling Windows, an entirely inappropriate course given that Microsoft's own validation tools report a genuine installation.
I ran a full scan using Windows Defender Offline, but it didn't solve the problem. On this particular system the malware bamboozled Microsoft Security Essentials.
Mediocre Malware Cleanup
On the malware-infested systems where Microsoft Security Essentials installed and ran correctly, a full scan took hours. Scanning my standard clean test system took 72 minutes, about twice the average. And despite these lengthy scans, the cleanup wasn't very thorough.
Microsoft Security Essentials detected 63 percent of the threats, lower than any product tested with the current or previous set of malware samples. It left behind executable files for more than half of those it did detect, and several of them were still running after their alleged removal. Its overall score of 4.3 points for malware cleanup is the lowest of any current product.
40 percent detection of rootkit samples is also a new low. However, Microsoft thoroughly cleaned up all the rootkits it did find, scoring 4.0 points. Quite a few products tested with the previous malware collection scored lower, despite higher detection rates. Even so, I wouldn't rely on Microsoft to clean up a malware-infested system.
Source : PCMAG.com