The Pennsylvania Department of Revenue is mailing letters to 865 taxpayers to let them know their personal information wasn’t properly secured on a laptop that’s been stolen.

The department said Tuesday that it is informing the victims about free credit monitoring services and fraud protections it’ll offer.

It says department auditors were in San Francisco in late June when thieves smashed the windows of the auditors’ rental vehicle.

Four laptop computers were stolen and haven’t been recovered.

The agency says law enforcement was notified immediately. While the department’s computer network hasn’t hacked, it says it found that some procedures to secure data weren’t followed with one laptop.