The U.S. Internal Revenue Service (IRS) said on Monday that the country made progress against identity theft, refund fraud and other tax misconduct in 2018, but more work remained to be done.

According to the federal tax collection agency, the number of identity theft victims that reported to the IRS dropped significantly in the past few years. IRS data showed that it received 199,000 identity theft reports from taxpayers in 2018, lower than the reading of 242,000 in 2017 and 401,000 in 2016.

Meanwhile, the IRS said it protected 3.1 billion U.S. dollars in fraudulent refunds in 2018, down from 6 billion dollars in 2017 and 6.4 billion dollars in 2016.

"At a time when many in the private sector continue to struggle with these issues, the tax community has made major progress working together to stop identity theft and refund fraud," said Chuck Rettig, the commissioner of IRS.

Even as it made some progress, IRS noted the new challenges brought up by the identity thefts.

The number of confirmed identity theft returns ticked up 9 percent to 649,000, which was higher than the reading of 597,000 in 2017, according to IRS.

Besides, the IRS noted that business identity theft and data theft from tax professionals may become new concerns as identity thieves change their targets and tactics.

"Identity thieves are often members of sophisticated criminal syndicates, based here and abroad," said Rettig, "they have the resources, the technology and the skills to carry on this fight."

"Despite these major successes, more work remains," Rettig added.