As duties under the U.K.’s Online Safety Act (OSA) related to tackling illegal content came into force Monday, the internet watchdog, Ofcom, said it has launched a new enforcement program focused on online storage and file-sharing services.

The regulator said its evidence shows that file-sharing and file-storage services are “particularly susceptible” to being used for the sharing of image-based child sexual abuse material (CSAM). The enforcement programme will assess safety measures they put in place that are aimed at preventing offenders from disseminating CSAM on their services.

Ofcom added that it has written to “a number” of these services, without naming any of those involved. It has put them on notice that “formal information requests” will soon be sent regarding the measures they have already implemented or plan to implement to tackle CSAM. It will ask them to submit illegal harm risk assessments.

Failure to comply with the OSA could lead to major penalties — of up to 10% of global annual turnover.