Hackers from the Anonymous group have claimed to have leaked Greek Ministry of Finance confidential documents, passwords and logins.
The purported hack was to protest the worsening economic conditions in Greece, which has seen tough austerity measures, according to a document posted on AnonPaste.
"We gained full access to the Greek Ministry of Finance," the group claimed in the document about #OpGreece.
Greece is in ongoing discussions with the European Union, the European Central Bank and the International Monetary Fund to agree a €13.5 billion package of cuts described by the Guardian as "draconian".
Anonymous claimed to be protesting about the fallout of austerity measures, including the increasing popularity and power of the far-right Golden Dawn party.
Anonymous posted a compressed file with documents, plus passwords and logins, that the group claimed were valid. Anonymous said it had accessed IBM servers, and that it possessed an SAP zero-day exploit.
The Greek Ministry of Finance said that it was investigating the validity of the Anonymous hack claims.
"There is an ongoing inquiry," a Ministry of Finance spokeswoman told SC Magazine UK on Tuesday. "We are searching to see if this [hack] happened."