It was meant solely to be a celebratory post by Mark Zuckerberg about Instagram reaching the milestone of 500 million users. But as CNET reports, the Internet was far more interested in what Zuckerberg revealed inadvertently: His laptop is in the background, and it shows that Zuckerberg puts a piece of tape over its camera as an apparent security measure—to ward off hackers who might gain control of it remotely to spy on him. A Twitter user named Chris Olson seemed to be the first to spot it, tweeting on Tuesday that Zuckerberg also tapes over his microphone jack and uses a rather obscure email client from Mozilla called Thunderbird. (Some think it's actually a Cisco VPN client.) Reaction: