The IRS is making it tougher for identity thieves to dupe the government and claim fraudulent tax returns—a problem the IRS says has grown “exponentially.”

In 2012, the IRS reported it stopped 5 million suspicious returns and prevented $20 billion in fraudulent returns, including returns related to identity theft—an increase from 3 million returns and $14 billion in 2011.

The government agency is increasing criminal sentences for those convicted of tax-related identity theft and creating new penalties for anyone filing bogus returns. It is also taking steps to limit access to Social Security Administration files on deceased individuals.

At the end of last year, the IRS had more than double the amount of employees working on identity theft issues than the year before. A total of more than 3,000 IRS employees were employed for this purpose at the end of 2012.