The IRS posted Form 990-T data from approximately 120,000 people with individual retirement account plans that earn certain types of business income, the report said.
The classified information included the taxpayer names, contact and financial information, but did not include Social Security numbers or other data that could impact their credit score, the report said.
The IRS attributes the incident to a human coding error that occurred last year when the 990-T Forms began to be electronically filed, the report said.
The mistake was discovered by an IRS research employee in recent weeks, leading to the removal of the data from public sites, the report added.
Affected taxpayers will be contacted in the coming weeks about the incident, according to the report.