The University of Maryland on Friday morning detailed the credit monitoring it is offering anyone affected by a computer security attack on the school that compromised hundreds of thousands of personal records.

The security breach early Tuesday morning exposed the names, Social Security numbers, dates of birth and university identification numbers for 309,079 people affiliated with U-Md. on its College Park and Shady Grove campuses. The attack targeted a secure database that holds information from as far back as 1998.

In a letter to the university community, U-Md. chief information officer Brian Voss wrote that the university is providing a free year of Experian’s ProtectMyID Alert, a service that tracks identity theft and other misuse of personal information. Faculty, students and staff can check whether their records were compromised or sign up for the credit monitoring by calling 1-866-274-3891, beginning Tuesday. The option will be available until the end of May.

Voss told the U-Md. community that the U.S. Secret Service has joined the investigation into the security attack. The school is also working with MITRE, a systems engineering company, to determine how the breach occurred and how to avoid similar events in future.

“We just continue to try to get to the bottom of how this was done,” Voss said Friday afternoon.