So as you've probably heard, and as mexicancouchpotato pointed out, there is something going around called the Blue Whale "game". This supposed "game" or challenge, takes course over 50 days and has several tiers of self harm, all leading up to day 50 where the end "goal" is suicide. It has caused many deaths in Russia and has a cult-like mentality. They command you to commit the self harm, then post a picture of it. If you refuse, they send you threats and say they'll kill your family. 

 BUT STAY CALM! It's spreading in the UK and in Russia but as far as my sources know, it hasn't touched the US yet. And they can only hack you if you respond to a message they sent. DO NOT RESPOND TO THEM! Don't even try to troll or be funny because as soon as you respond they can hack into your phone and get your information. They can only hack you if you respond, so don't respond to any weird or creepy messages you receive on Instagram, Tumblr, or any other media for that matter. 

Stay safe everyone. 

If you want more information, mexicancouchpotato has published warnings on it in most of his books, and did a better job than me explaining this, so go look at the information he has.