When is a leak not a leak? When it comes direct from the source, which in this case would be Microsoft, and the product in question would be the much-anticipated Windows 8.1 Update 1. I guess you'd technically call that a whoopsie doodle.
The update had already leaked to torrent sites -- reportedly the work of folks in Russia, who claim Microsoft finalized it in late February -- but when it showed up in the Windows Update service Thursday, all eyes turned to Redmond. The update went out to manufacturers earlier this week, but no one expected it to show up on on Microsoft's own publicly accessible servers yesterday.
ZDNet says the update was supposed to roll out gradually -- first to insiders, and only at the end of the line to the general public. Instead, someone at Microsoft apparently pulled the public trigger early, or at least opened a backdoor that should have remained closed: In order to access the update, you had to either fiddle your registry settings, or track down direct links provided by someone in a popular online computing forum. ZDNet confirmed the authenticity of the registry edit retrieval method, noting it was able to execute the update on a Surface Pro running Windows 8.1 Pro, though the process apparently failed on a desktop running Windows 8.1 Enterprise.
Microsoft has since put the kibosh on obtaining the update directly, though a few sites are reporting the necessary files are now being hosted by users who managed to pull them down. I assume they'll also hit the torrent scene posthaste, if they haven't already.
In any event, you're probably best waiting for Microsoft to unveil the update officially. Early access to something sounds alluring...until it breaks your system and no one's available to help you un-break it, since it's not yet formally supported.