H&R Block Inc. last month mistakenly mailed out free copies of its tax return software that included the recipients’ Social Security numbers on the mailing label, the Kansas City, Mo.-based company said Wednesday.

Fewer than 3 percent of the TaxCut mailings had the numbers, and the company said it began mailing letters on Dec. 22 warning recipients about the mix-up and created a Web site for questions.

The numbers were embedded in a string of 47 numbers and letters printed above the mailing code. Because the numbers weren’t broken out identity thieves were less likely to have exploited it, the company said.