Mark Zuckerberg TOPLESS Photo -- Privacy Malfunction?

A photo of a topless Mark Zuckerberg is burning up the Internet right now ... immediately fueling suspicions of a major Facebook privacy screw-up.

It's unclear when or where the pic was taken ... showing the kid billionaire sans shirt with a couple of male friends. Mark's in pretty good shape for a computer nerd.

Now for the conspiracy theory ...

The image surfaced on the image-sharing site imgur ... along with a photo caption that appears to explain how the anonymous poster got a hold of the shot in the first place.

The poster claims the pic was "accidentally posted" by Facebook Director of Engineering Andrew Bosworth ... who also appears in the pic on the far right.

The poster claims Bosworth deleted the pic "seconds later" ... but it was too late, someone captured the image and splashed it to the web.

If so, it would be another black eye for the social network ... which is still trying to recover from its epically poor performance on the stock market.

We've reached out to Facebook -- so far, no comment.