20 Hate all heretics, but especially him who is rightly named after mania, who arose not long ago in the reign of Probus. For the delusion began full seventy years ago, and there are men still living who saw him with their very eyes. But hate him not for this, that he lived a short time ago; but because of his impious doctrines hate thou the worker of wickedness, the receptacle of all filth, who gathered up the mire of every heresy. For aspiring to become pre-eminent among wicked men, he took the doctrines of all, and having combined them into one heresy filled with blasphemies and all iniquity, he makes havoc of the Church, or rather of those outside the Church, roaming about like a lion and devouring. Heed not their fair speech, nor their supposed humility: for they are serpents, a generation of vipers. Judas too said Hail! Master, even while he was betraying Him. Heed not their kisses, but beware of their venom.
Source: Catechetical Lectures (New Advent)