Some taxpayers seeking a quick refund may have to wait longer than usual this year as the Internal Revenue Service tries to stop criminals who steal others’ identities and file fraudulent returns.

The agency, which began accepting 2012 returns Wednesday, is making its system more sensitive to signs of potential fraud, meaning some returns will get a closer look. Last year, the IRS prevented $20 billion in fraudulent refunds from being issued, up from $14 billion in 2011.