Microsoft Security Essentials (MSE) beta build 1.0.1500.0 has quietly appeared out of nowhere today. There's no official announcement, testers haven't received any e-mail notification, and it's unclear if this is the second public build, either a Beta Refresh or a Release Candidate, which the software giant promised to release this summer.
There's a few more odd things with this release, such as the fact that the update points to KB article 972958, which doesn't appear to exist, at least not at the time of publishing. Furthermore, some users are reporting that they are actually getting build 1.0.1501.0 instead of 1.0.1500.0 when they update. The new version is available for current MSE testers on the Downloads section of the Microsoft Security Essentials beta program on Microsoft Connect, although the release date mistakenly says the build was posted on June 21, 2009. On Connect, the version is also mistakenly referred to as 1.0.1500.0 but the actual installers are for 1.0.1501.0. The new build was also released as an optional update on Windows Update, with today's date stamp, and that update really gets you build 1.0.1500.0: