A twenty-year-old Bulgarian national was detained in connection with the hacker attack against the servers of the National Revenue Agency. The suspect is employed at a cybersecurity company and was testing security networks and computer systems. The investigators are analyzing encrypted information in the computers seized by the law enforcement authorities. Traces leading to the hacker attack against the National Revenue Agency were already found in some of them. The people behind the criminal act are Bulgarians, the spokesperson of the National Revenue Agency Rosen Bachvarov announced. We suppose that the letter sent to the media by a Russian national was not written by the real perpetrator of the hacker attack, Rosen Bachvarov added.