SOFIA, Bulgaria -- Bulgarian police have detained a suspect who is allegedly behind the hacking of the national revenue agency, an attack that leaked the personal and financial data of millions of Bulgarians and companies.

Police cybersecurity chief Yavor Kolev said Wednesday a 20-year-old Bulgarian employee of a cybersecurity company is suspected in the hacking.

The leak is the biggest in the Balkan nation so far. Local media say the details of some 5 million of the country's 7 million people were stolen.

Kolev said the investigation is still ongoing and other people could have been involved.

Prime Minister Boyko Borissov said the well-educated suspect was trying to prove his computer skills. Borissov added the suspect was a credit to Bulgaria's education system but he should have been working for the state instead of causing harm.