The airport scanners that let TSA agents see through travelers’ clothes can be fairly easily obstructed from detecting concealed weapons or bombs, according to researchers from several top U.S. universities.

The study, to be presented at the Usenix security conference in San Diego, shows that the Rapiscan Security 100 Single Pose full-body “backscatter” scanner (which the TSA discarded last year) can be breached by covering contraband beneath simple plastic shields and under clothing. The scanner’s software can also be hacked to present images at certain angles or to cover up certain sections of the body, Businessweek reports.

While these particular scanners are no longer in use in airports, the conference presenters pointed out that they were sold at deep discounts to other government facilities, such as courthouses and prisons, and they remain in use at airports around the world.