U.S. border officials seized and searched nearly 15,000 computers, phones and tablets over the last six months as the federal government stepped up its traveler surveillance, saying it’s responding to the latest public safety threats.

While only a tiny fraction of travelers face the intrusive scrutiny — less than a hundredth of one percent — the number has been steadily growing.

In 2015, U.S. Customs and Border Protection (CBP) seized electronic devices at a rate of about 23 a day. By this year, it was seizing them at a rate of 82 per day.

The searches include both U.S. citizens and legal permanent residents returning to their homes from trips abroad, as well as visitors and new immigrants arriving for the first time.

“The increase of electronic device searches is driven by CBP’s mission to protect the American people and enforce the nation’s laws in this digital age,” the agency said in a statement announcing the new figures.

“CBP has adapted and adjusted its actions to align with current threat information. CBP border searches of electronic devices have resulted in evidence helpful in combating terrorist activity, child pornography, violations of export controls, intellectual property rights violations, and visa fraud,” the agency said.

Officials have been unable to say, however, how many of the searches involved potential terrorist activity, nor could officials say what percentage of those being subject to the search were U.S. citizens.

Usually the seizure is a quick check, but CBP also claims the power to hold onto the item for a more thorough forensic search.

Civil liberties groups say CBP is treading on dangerous ground, and predicted an increase in court challenges.

All told, CBP searched some 14,993 electronic devices between Oct. 1 and March 31. That’s far higher than the 8,383 searched during the same period a year earlier, and about equal to the whole level of searches done in all 12 months of fiscal year 2015.

The 2015 and 2016 numbers are updates to what CBP released just a couple of months ago. The agency said the previously released numbers were wrong, blaming “an anomaly” in the tracking system that attached the wrong date to some searches, boosting the 2016 number beyond what it should have been.