What in the world is going on with Microsoft's Visio? Poster rseiler, on the Windows Update blog, was the first to mention a supremely weird patch for Visio 2013 offered on the Windows Update site. Researchers are looking into the gargantuan patch and trying to figure out exactly what it contains.

Here's how rseiler put it:

Today's Office updates brought an interesting one, sized 481.4MB, which I thought was WAY larger than any Office component should be (the entire 2013 ProPlus install is about 700MB). Then I realized that I don't have Visio installed at all, which is a separate product from Office ProPlus (just like Project). Why is it being offered? Is MS suddenly giving away Visio? The KB article isn't posted yet. BTW, this is not to be confused with the tiny Visio Viewer, which is also offered.

In fact, Visio Pro with XP1 in the 64-bit version, with an EXE installer, runs 464MB.

Microsoft's Download Center documents the download:

Microsoft has released an update for Microsoft Visio 2013 64-Bit Edition. This update provides the latest fixes to Microsoft Visio 2013 64-Bit Edition. Additionally, this update contains stability and performance improvements.

A quick look at the Details section on that page reveals that the download is "Version 1.0" with a file name of visio2013-kb2837632-fullfile-x64-glb.exe -- and a release date of April 1.

If you click through to the purported KB article, 2837632, there's a Page Not Found error. It looks like it's an April Fools' Day joke, right?

No, not exactly. Microsoft's official April 2014 Office Update Release page on TechNet lists this under Non-Security updates:

To improve search functionality, and to improve compatibility with international fonts in Visio: Update for Microsoft Visio 2010 (KB2553444) Update for Microsoft Office 2013 (KB2863843) Update for Microsoft Visio 2013 (KB2837632) Update for Microsoft Visio Viewer 2013 (KB2817301)

If KB 2837632 is a joke, it was slipped into the official release notes.

By comparison, the Visio 2010 update runs 19MB.

MVPs on the Answers Forum are currently trying to figure out what in the world is going on. In the interim, it would be wise to avoid installing the patch -- or the joke. t/h SB

This story, "Is Windows Update's huge Visio 2013 patch a joke?," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest developments in business technology news, follow InfoWorld.com on Twitter.