Over 7,000 people were investigated for online sex crimes between 2021 and 2023, but only 5.5 percent of them were detained, police data showed Tuesday.

A total of 9,864 such crimes occurred in that period, according to National Police Agency data submitted to Democratic Party Rep. Hwang Jung-a. A total of 3,295 of them were related to child pornography -- accounting for 43.8 percent -- followed by 2,415 cases involving illegally filmed content and 1,563 cases involving other illegal pornography.

Of the thousands investigated for the crimes, only 412 were taken into custody.

There were 257 sex crimes involving deepfake technology in the three years, accounting for just 3.4 percent of the total. But the data showed the number was rising. There were 156 cases involving deepfake technology in 2021, but 297 between January and July of this year.

As in case of other cyber sex crimes, the percentage of deepfake suspects who were detained was also low. A total of 257 people were investigated for fake video crimes in 2021-23, but only 12 were taken into custody.

Of the 146 people investigated for deepfake crimes this year, only four were detained.

"Digital sex crime should be treated severely, as it can be committed easily with just smartphones and computers and spreads very fast," Hwang said. "Investigative organizations have had tendency to underestimate the gravity of the damages (caused by cyber sex crimes), and there hasn't been proper response (to such crimes)."

She called for a comprehensive measure encompassing prevention of the said crimes, the punishment and aiding the victims.