A hacking group dubbed CryptoCore has stolen more than $200 million in virtual currency from several cryptocurrency exchanges over the past two years, the security firm ClearSky Cyber Security reports. The CryptoCore gang has used spear-phishing emails and social engineering techniques to target employees and executives at cryptocurrency exchanges, mainly in the U.S. and Japan, according to the ClearSky analysis. Without offering specifics, the analysts note that they have a “medium level of certainty” that CryptoCore most likely operates out of Ukraine, Russia or Romania. The hacker group is also known by the names “Dangerous Password” and “Leery Turtle.”