The tens-of-thousands of Taxpayer Form 990-T were temporarily available for public viewing on the IRS website.
Individuals file the form to disclose certain types of income within their retirement accounts.
The forms included the names and contact information of the filers, as well as significant part of their financial records.
Treasury made clear, however, the briefly available information did not include Social Security numbers.
“The Treasury Department has instructed the IRS to conduct a prompt review of its practices to ensure necessary protections are in place to prevent unauthorized data disclosures,” agency told Congress on Friday.