Tax returns of more than 100,000 U.S. taxpayers have been exposed in a breach of the Internal Revenue Service's online "Get Transcript" service, the IRS reported today. Tax returns include a variety of sensitive information on individuals, including Social Security numbers, dates of birth, addresses, spouses' identity information, and employment data.

The agency told the Associated Press that attackers made about 200,000 attempts to access records through the service, "with more than 100,000 of those attempts successfully clearing authentication hurdles." Successful authentication required a variety of knowledge about a taxpayer including Social Security number, date of birth, tax filing status, and street address, according to the agency.

The agency says the system was accessed between February and mid-May. They have not yet provided any attribution.

For more information, see the Associated Press story here. DarkReading will follow up with more details as they become available.