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9. Microsoft Windows Update (1998 to present)

Yes, we know, our computers would be even more vulnerable if we didn't use Update to plug Windows' seemingly endless security holes. But using it to distribute Microsoft's Windows Genuine Advantage tattleware puts Update firmly in the annoyance column (not to mention the way it autorestarts your system after it's done installing). Delivered as a "critical" update last spring, WGA installed itself with minimal notice, secretly phoned home with information about users' systems, and wrongly identified possibly millions of legitimate copies of Windows XP as pirated. No one likes a rat, and clearly that's the sentiment our readers hold toward this otherwise reasonably useful service.