“What the investigators found inside Nasdaq shocked them, according to both law enforcement officials and private contractors hired by the company to aid in the investigation. Agents found the tracks of several different groups operating freely, some of which may have been in the exchange’s networks for years, including criminal hackers and Chinese cyberspies. Basic records of the daily activity occurring on the company’s servers, which would have helped investigators trace the hackers’ movements, were almost nonexistent”

http://mobile.businessweek.com/articles/2014-07-17/how-russian-hackers-stole-the-nasdaq