This may be the most brutally effective Facebook prank of all time

If ever there was a good reason not to leave your Facebook unguarded around pesky friends and family members, it's this.

On Monday, Kevin Keenan of Castlewellan, Northern Ireland, shared a cheerful message on Facebook. Basically, Keenan said that he had two tickets to give away to the All Ireland Football Final (a very popular annual Gaelic football tournament), and anyone who tagged a friend in the comments could be in with a chance of winning:

Original image has been replaced. Credit: Mashable

The giveaway worked like a charm. People quickly began tagging their friends and sharing the post, and at the time of writing it's received well over 1,000 shares and 1,300 comments in two days.

The only problem? Keenan didn't actually write the post, and he definitely doesn't have any tickets.

Finally noticing on Monday evening that something was amiss, Keenan shared the following update:

Original image has been replaced. Credit: Mashable

Yep, the whole thing was a massive prank. Presumably Kevin made the mistake of leaving his Facebook page open, and Marty -- sensing the perfect opportunity -- pounced.

The whole thing quickly escalated, and was made even worse by the fact that Kevin posted a separate status explaining it was a prank, rather than commenting on the original post so people looking at a shared version could see it wasn't real (at the time of writing, people are still tagging their friends under the original).

You've got to hand it to Marty, really -- it's not often that a throwaway Facebook status prank ends up fooling more than 1,000 people.