The IRS recently identified and halted an automated attack upon its Electronic Filing PIN application on IRS.gov. Using personal data stolen elsewhere outside the IRS, identity thieves used malware in an attempt to generate E-file PINs for stolen social security numbers. An E-file pin is used in some instances to electronically file a tax return. No personal taxpayer data was compromised or disclosed by IRS systems. 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. Based on their review, they identified unauthorized attempts involving approximately 464,000 unique SSNs, of which 101,000 SSNs were used to successfully access an E-file PIN. The incident, involving an automated bot, occurred last month, and the IRS continues to closely monitor the web application.