Microsoft Security Essentials: Why jump from 2 to 4?

Previously, I mentioned that Microsoft Security Essentials v4.0 is on its way, though there is no version 3.0. Well, I think I discovered the reason behind the version hop. Here are two screenshots from About dialog boxes of Microsoft Security Essentials v2.1 on Windows 7 and Microsoft Security Essentials v4.0 Beta on Windows XP, which help shed a light on the matter.

Microsoft Security Essentials 2.0 – About dialog box

Microsoft Security Essentials 4.0 Beta – About dialog box

There are a handful of version numbers listed in each dialog box but the only two that concern us are Security Essentials Version and Antimalware Client Version. In Microsoft Security Essentials v4.0, both version numbers are 4.0.1113.0. In Microsoft Security Essentials v2.1 however, the Security Essentials Version is 2.1.1116.0 while the Antimalware Client Version is 3.0.8402.0.

According to Microsoft, all modern Microsoft antivirus products use the same antimalware engine. While the graphical user interface of v2.1 (msseces.exe) dates back to 16 June 2011, its antimalware engine (MsMpEng.exe, MpCmdRun.exe and NisSrv.exe) is updated on 28 April 2011. (Check the included digital certificates on the mentioned files.) In v4.0 however, both the engine and the client are new. It is my guess that Microsoft meant to unify the version numbers with this new release, just as it did to Movie Maker and Microsoft Office products.