When were the Gnostics first considered heretics?

[EthAdCinviDeco]

Yeah, just a quick question for some research I'm doing. All I can find at the moment are some notable 'hunters' and that's about it. So yeah, thanks =D

[Logomachist]

As I understand it, it's not so much that Gnosticism suddenly became a heresy, it's that other Christian factions, which always had opposed Gnostic teachings, came to dominate and gnosticism rapidly dwindled. What became the Roman Church had argued against it from the start.