The State Department recently suffered a breach of its unclassified email system, and the compromise exposed the personal information of a small number of employees, according to a notice sent to the agency's workforce.

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State described the incident as "activity of concern … affecting less than 1% of employee inboxes" in a September 7 alert that was shared with POLITICO and confirmed by two U.S. officials.

"We have determined that certain employees' personally identifiable information (PII) may have been exposed," the alert said. "We have notified those employees."

The classified email system was not affected, according to the alert, which was marked "Sensitive But Unclassified."

Following the email breach, the department convened a task force to examine the incident, according to a U.S. official, who requested anonymity to discuss a security matter.