My understanding of hacker is specifically someone who exploits vulnerabilities in code. Regular programmers are like building architects, hackers are like people holding up a mask so that the facial recognition powered NEST lock will let them inside the building.
so what do we call undesirables like anonymous and so on?
"cracker" or "security hacker"
"crackers" or "security hackers". I'm sure most people on this site would consider themselves to be some form of "hacker", after all, this is "Hacker News".