The Internal Revenue Service (IRS) has dramatically increased the number of citizens impacted by the May 2015 breach to 700,000 from the original 114,000 originally announced.

The additional victims were discovered during the IRS' on-going investigation into the the breach. The IRS found and additional 390,000 taxpayer accounts were potentially accessed and that the hackers had unsuccessfully targeted another 295,000 taxpayer transcripts, the IRS said in a statement.

The hackers initially accessed the IRS system through its 'Get Transcript' application, which went online in January 2014, using information from an outside source, the IRS said. The app has been offline since the attack and the IRS will begin sending out letters to the victims starting on Feb. 29, 2016.