A Los Angeles man Wednesday pleaded guilty to using spyware that turned thousands of computers across the United States into “zombies” so he could steal their owners’ identities

John Schiefer, who worked as a computer security expert, “admitted that he gained access without authorization to hundreds of thousands of computers in the United States and that he remotely controlled these compromised machines through computer servers,” federal prosecutors said in a statement.

He was charged under the Federal Wiretap Act, Assistant U.S. District Attorney Mark Krause told SCMagazineUS.com on Thursday. Scheifer was freed on bond. He faces up to 60 years in federal prison and $1.75 million in fines when he is sentenced Aug. 20.