DUBUQUE, Iowa (AP) — Officials in one eastern Iowa county are trying to track down $524,284 they believe was stolen when an employee transferred it in response to a fake email message that appeared to be from the city of Dyersville.

Dubuque County officials announced the money was missing Monday, according to the Telegraph Herald.

The county auditor and sheriff learned the money was missing when Dyersville officials asked about the status of the transfer after the county had already made it.

Auditor Kevin Dragotto said in a statement that an internal review determined that the city of Dyersville’s email system had been compromised. Dragotto said county employees received a request for the money from an official Dyersville email address, and the payment was sent.

The auditor’s office said officials now believe that invoice was “orchestrated by a third party.”