But there were also false prophets among the people, just as there will be false teachers among you. They will secretly introduce destructive heresies, even denying the sovereign Lord who bought them – bringing swift destruction on themselves. (NIV)

BUT ALSO [in those days] there arose false prophets among the people, just as there will be false teachers among yourselves, who will subtly and stealthily introduce heretical doctrines (destructive heresies), even denying and disowning the Master Who bought them, bringing upon themselves swift destruction. (AMP)

But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction. (KJV)