A Kosovo citizen has pleaded guilty to hacking computers to expose U.S. service members' personal data on behalf of the Islamic State.

At a plea hearing Wednesday in federal court in Alexandria, Virginia, 20-year-old Ardit Ferizi told a judge that he still doesn't know why he committed the crime. He pleaded guilty to providing material support to ISIS and unauthorized access to a computer.

British-born ISIS operative Junaid Hussain later exposed the data Ferizi uncovered in a social media campaign that urged the group’s followers to target those service members. A U.S. drone strike killed Hussain last summer.

Ferizi faces up to 25 years in prison when he is sentenced in September.

Ferizi admitted hacking the records of a private company and providing names, email passwords and phone numbers of more than 1,300 service members to ISIS last year. Upon publishing the data, the terror network warned it would "strike at your necks in your own lands."

Fox News' Matt Dean and The Associated Press contributed to this report.