Microsoft has quietly issued a second version of its free Security Essentials suite.
The software was slipped out without any press release or announcement on the Microsoft Security blog, despite containing a series of new features and improvements.
Although users would be hard pressed to notice any visible changes, there has been notable work taking place beneath the surface.
The antivirus engine has benefited from the same upgrade applied to Microsoft's paid-for Forefront Client Security suite for businesses.
The new engine offers "efficient threat detection against the latest malware and rootkits" and "protection against 'unknown' or 'zero day' threats through behaviour monitoring and emulation", according to Microsoft.
One reason why Microsoft might not have decided to draw attention to the upgrade is the new integration with the Windows Firewall. Users are now asked whether they want to turn on the Windows Firewall during installation, dragging Security Essentials closer to becoming a full fledged security suite, rather than the standalone antivirus app it was originally.
Rival security firms Panda and Trend Micro recently complained about Microsoft's "anti-competitive" behaviour with Security Essentials, after the software was included in Microsoft Update. Panda called for a Windows security ballot, similar to the one offered for internet browsers.
Microsoft Security Essentials 2.0 is available for download here. It was not currently being offered via the software's own upgrade mechanism.