The attack was on the Pentagon’s Joint Staff unclassified email system which has since been taken offline for the past two weeks. US officials are claiming that the attack took place on the 25th of July and has since affected about 4,000 military and civilian personnel who work for the Joint Chiefs of Staff.
That being said, the attack was said to have been carried out by an automated system. This system is apparently capable of gathering huge amounts of data, like those found in emails, and then quickly distribute it to thousands of accounts in the cloud so as to spread the data around as opposed to storing it all in one place.
While it is unclear as to whether or not the Russian government was directly involved in the cyberattack, NBC learnt from US officials that it was definitely the work of a state actor. They also add that thankfully no classified information had been stolen or compromised in the hack.