UPDATE 1-Bulgarian cybersecurity worker detained over tax agency hack attack

A 20-year-old Bulgarian cybersecurity worker has been arrested on suspicion of involvement in a hacking attack that stole millions of taxpayers' personal and financial data, interior ministry officials said on Wednesday.

The man, who works for a company that protects IT systems against breaches, was detained on Tuesday afternoon, police cybersecurity chief Yavor Kolev said. Finance minister Vladislav Goranov apologized to the country on Tuesday for the attack on servers at the tax agency (NRA), which one researcher said may have compromised nearly every adult's personal records.

Kolev said investigations were still at an early stage and police were still looking into the possibility that other people were involved. Officers seized a laptop and other devices from the suspect's office and home in Sofia and found encrypted data, Kolev added.

"We have detained a suspect. His job was to test computer systems and networks for possible vulnerabilities to prevent attacks," Kolev told bTV television. The attack on the tax agency happened at the end of June and compromised about 3% of its databases, officials said. A person claiming to be a Russian hacker emailed local media on Monday offering access to the stolen data.