Badvocate

Taking such a transparent, honest approach can even provide "an opportunity to change a badvocate, into a potential advocate,” says Bough, as long as communications are authentic and sincere.

Source: wiktionary

In this case, a company ought to determine whether an individual who discusses company products is a valuable marketing resource (advocate) or a threat to the brand (badvocate).

Source: wiktionary

One type of badvocate, sometimes identified as a troll, is a hacktivist.

Source: wiktionary