[hedgetrimmer]

Main Entry: in·sur·gent
Pronunciation: -j&nt
Function: noun
Etymology: Latin insurgent-, insurgens, present participle of insurgere to rise up, from in- + surgere to rise -- more at SURGE
Date: 1765
1 : a person who revolts against civil authority or an established government; especially : a rebel not recognized as a belligerent

[visualops]

I thought of insurgent but to me that implies a more open confrontation, and the problem with the enemy within is they appear, or attempt to appear, as the 'good' guys (~we just want peace~~ blah blah). That's why I felt subversive was a better word to start with.