The Chinese hackers who breached the Office of Personnel Management last year used superhero names out of the Marvel Comics universe, according to a congressional report released Wednesday.

The hackers first registered the domain “opmsecurity.org” to “Steve Rogers, a.k.a. ‘Captain America,'” in April 2014, according to investigators on the House Oversight Committee. The name was later used as a “command and control” domain to direct malware in the agency’s systems.