Congressional investigators say Social Security has made more than $1 billion in improper disability payments to people who had jobs when they were supposed to be unable to work.

In a report, the Government Accountability Office estimated that 36,000 workers got improper payments from December 2010 to January 2013.

The numbers represent less than 1 percent of beneficiaries and less than 1 percent of disability payments made during the time frame. But GAO says the overpayments reveal weaknesses in Social Security's procedures for policing the system.

In a written response to the report, the Social Security Administration said it has an extremely high accuracy rate for disability payments but noted that even small errors translate into big numbers. The agency questioned whether GAO overestimated the amount of overpayments.