An automated attack on the IRS' computer systems in January used stolen personal data to create fake logins through the agency's Electronic Filing PIN service.
About 464,000 Social Security numbers were used in the attack on the IRS.gov system, the agency said late Tuesday, and 101,000 of those numbers allowed the attackers to get at an E-file PIN. The PIN can be used to electronically file a tax return.
"No personal taxpayer data was compromised or disclosed by IRS systems," the IRS said in a statement Tuesday. "The IRS also is taking immediate steps to notify affected taxpayers by mail that their personal information was used in an attempt to access the IRS application. The IRS is also protecting their accounts by marking them to protect against tax-related identity theft."