Konami officially launched the online component for Metal Gear Solid V: The Phantom Pain, Metal Gear Online, for the PC on Steam earlier today, but the feature has already been shut down.
According to Konami community manager Robert Peeler, the reason behind the online service being pulled was due to a "possible exploit." Once the exploit is removed, the beta will return to Steam.
“Due to a possible exploit, we’ve removed access to the Beta temporarily while a hotfix is being prepared,”Peeler wrote on Steam forums (via Kotaku) "Once the issue is addressed we’ll provide access to the Beta once again.”
Reports say the exploit allowed players to purchase MB coins for free. This might not sound like a big problem, but for Konami it is. MB coins can only be purchased through microtransaction, of course, if you don't want purchase them you can win them through Daily bonuses and save them up (it just takes longer to accrue all the coins you need).