The personal information of about 16,000 South Koreans employed by the U.S. military may have been compromised in a hacking attack on two databases, the military said Thursday.

Gen. Curtis M. Scaparrottti, the top U.S. military official in South Korea, sent a letter Thursday to South Korean employees apologizing for the data breach, which was discovered last week, according to a statement. The hack may have exposed personal information, including contact information, education, work experience and Korean Identification Numbers.

“We deeply regret and apologize for any inconvenience and concern this matter may cause you,” Scaparrotti said in the letter. U.S. Forces Korea “takes this potential compromise very seriously and is reviewing policies and practices with a view of determining what must be changed to preclude a similar occurrence in the future. The safety and protection of our employees’ personal information are paramount to USFK.”

The military said there was no banking or credit card data stored on the databases, and no military or defense-related information was compromised because the databases that were hacked are on a different system than U.S. Forces Korea’s military network.

More than 16,000 South Koreans who are employees or former employees, and those who applied for a job with U.S. Forces Korea may have been affected by the breach, according to the military, which said it would offer a credit-monitoring service to any potential victim that requests it.