I recently received an email from LinkedIn claiming that it was sent at the request of a friend of mine. But it turns out that the person in question had not asked LinkedIn to send me an invitation. So how did this happen?
A bit of searching reveals that LinkedIn offers its users an option to check who you might know on LinkedIn. But what this actually does is to search your email address book and send messages to everyone in it, claiming falsely to be from you, and inviting them to join LinkedIn. Apparently there's some fine print somewhere saying that it does this, but the LinkedIn people don't make it obvious.
Needless to say, I won't be doing any business with LinkedIn.
For more, see this discussion on LinkedIn's own website.
See also this from The Daily Show:
Update: For some reason this isn't the same video I originally linked to. That one included a rant by John Oliver against incessant spam from LinkedIn. But just about anything from The Daily Show is worth seeing, so enjoy...