Just to clarify something, unless you're reporting a spambot in chat, screenshots will not be enough evidence against a hacker. We require all hacker reports to have unedited
video evidence uploaded as an unlisted video to Youtube.com.
Additionally, do not confront a hacker. The best course of action would be to record them and posting the evidence at
http://www.minecraftsurvivalgames.com/forums/report-abuse/ or call for a moderator in the hub or poke one of us on Teamspeak. Include the hacker's name, the hack you suspect they're using or what they're doing, and the server (assuming they're in your game, you can find out what server you're in with /i).
Confronting them is a negative thing because they might try to report you for harassment which would be unfortunate or they'll turn the hacks off and go unpunished since there's no evidence against them.