And you thought tax season was stressful.

This week the IRS discovered it had experienced a data breach, according to the AP. Hackers stole the information of more than 100,000 people through online system provided by the agency called "Get Transcript" that lets users view their previous tax returns and other filings. The system was targeted from February to May of this year, with about 200,000 attempts made by the hackers to get the information from the system.

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To get into the system, the hackers had to know taxpayer's birthdates, tax filing status, address, Social Security numbers and additional personal security questions. Tax returns often have the information of not only the person filing but of their dependents as well.

“We’re confident that these are not amateurs but organized crime syndicates that not only we, but others in the financial industry are dealing with" said IRS Commissioner John Koskinen.

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Koskinen said in a press conference this week that the "Get Transcript" system had been shuttered for the time being. While this application was hacked, the agency's main computer wasn't affected. The organization estimates that it has processed " fewer than $15,000" of the fraudulent tax returns filled out with this stolen information, leading to $50 million in refunds.

In a statement yesterday, the agency said that it will be sending letters to all 200,000 people involved in the hack (whether the account was breached or it was attempted to be accessed). It is also offering free credit monitoring for those whose information was stolen. The IRS' criminal investigation unit and the treasury inspector general for tax administration are conducting investigations into the breach, and Congress will likely begin holding hearings soon.

Related: How to Respond to a Letter From the IRS? Breathe.