The Internal Revenue Service revealed hackers gained access to personal information for more than 700,000 individuals, more than twice as many as previously thought.
The breach was discovered last May. Hackers potentially stole Social Security numbers, birth dates and other information that could be used for identity theft.
The IRS said the hackers used taxpayer information acquired from outside the IRS to answer personal identity questions to access tax return information.
The agency seems to be slowly realizing how bad the hack actually was. When the breach was first revealed in May, it said more than 114,000 accounts had been accessed; then, it disclosed another 220,000 compromised accounts in August. It added another 390,000 to that total this week bringing it up to around 724,000.
It also disclosed a separate security breach earlier in February. In that instance, hackers used stolen Social Security numbers to create over 100,000 E-file PINs, which are used so individuals can file a tax return online.
The IRS says it is notifying anyone whose personal information was stolen through the mail, as well as offering free identity protection for a year.
This video includes images from Getty Images.