Bulgarian officials said Tuesday that unidentified hackers have stolen the personal details of millions of people from Bulgaria's national revenue agency and noted a possible Russian link in the case.
Prime Minister Boyko Borissov called an emergency meeting of all law enforcement services to consider the potential harm to the country's national security.
Finance Minister Vladislav Goranov told reporters after the meeting that the hackers behind the breach contacted local media using a mailbox from a Russian domain.
The leak, the biggest in the Balkan country, contains names, personal data and the financial earnings of individuals and companies. According to local media, the hackers have stolen the details of some 5 million of the country's 7 million people.
Goranov said the government has requested help from the European Union's cybersecurity agency.
Speaking to the bTV channel, Interior Minister Mladen Marinov said the attack coincided with Bulgaria's purchase of US F-16 fighter jets for its air force and that it could likely be motivated by that.
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"Organised criminal groups involved in cyberattacks usually seek financial profits, but here political motives are possible. The government decided yesterday to buy F-16 jets," Marinov said.
The finance minister, however, rejected a possible link to the jet purchase, saying the cyberattack had occurred before the deal was approved.
Bulgarian media, which received an email from the hackers, said it came from Russian mail provider Yandex.
The email also called for the release of WikiLeaks founder Julian Assange, who is now in a British prison serving a 50-week sentence for jumping bail in Britain and also faces an extradition request by the United States, which seeks him on espionage charges.
Bulgarian media quoted the hackers' email as criticizing the Bulgarian government and saying "the state of your cybersecurity is a joke.