A U.S. congressional probe into the impact of a hack of Juniper Networks Inc software will examine the possibility that it was initially altered at the behest of the National Security Agency, a lawmaker said in an interview on Thursday.

The House Committee on Oversight and Government Reform this month sent letters asking some two dozen agencies to provide documents showing whether they used Juniper devices running ScreenOS software. The company said in December ScreenOS had been compromised by hackers using a so-called back door in the software.

Rep. Will Hurd, a Texas Republican who heads the committee's technology subcommittee and formerly worked for the Central Intelligence Agency, said his initial goal in pursuing the probe was to determine whether government agencies, many of which use Juniper gear, had been compromised by the hackers.