A strange – and possibly harmful – update started being delivered to Windows computers yesterday. Early speculation ranged from problems with the Windows Update infrastructure to the service being compromised by attackers.

Microsoft eventually weighed in, saying that the update was part of a test, and that it was never intended to end up on user computers.

Apparently the update was installed on some Windows 7 computers, at least one of which was rendered nearly inoperable, according to the user.

Presumably there will be additional followup from Microsoft. This is the kind of problem that makes people (including myself) justifiably nervous about the forced automatic updates in Windows 10.

Ars Technica has additional details.