I have had a disturbing issue at work for a couple of days. Once every hour, a black window (probably a CMD window) would pop up for a fraction of a second on the screen and then disappear. I had no idea whether this was a virus, spyware, some other kind of malware or something benign.
Fortunately, a colleague of mine had the google skills to find the cause and the solution to the problem. It turned out this was caused by a scheduled task from Microsoft Office called OfficeBackgroundTaskHandlerRegistration. By starting the Task Scheduler and drilling down to Task Scheduler Library -> Microsoft -> Office, this task is shown and it can be disabled by right clicking on it and selecting Disable:
Some more googling reveals that this is a bug Microsoft is aware of and that it probably will go away in some future update: