SAN FRANCISCO — As so-called Patent Trial and Appeal Board trolls attract attention for using the threat of inter partes review proceedings to extract settlements from patent owners, another one of their targets is firing back.

CRFD Research filed subpoenas against Iron Dome, a defensive patent aggregator that threatened to challenge a patent CRFD is relying on in patent litigation against Hulu LLC, Netflix Inc. and Spotify over a software transfer method.

Iron Dome filed an IPR petition against CRFD after warning it in August that it would do so unless CRFD granted it transferable licenses. CRFD Research, a subsidiary of Marathon Patent Group, subpoenaed Iron Dome on Dec. 30 in the Delaware federal court case against Hulu, Netflix and Spotify.