whats the best way to remove backdoor gmod addons

I know the danger when installing leaked addons on nulledbb or anywhere in diaper, its my fault
but haha it was kinda weird and funny at the same time, I installed an addon i dont know which exactly and then a french guy popped up in my server and tried to execute scripts (i assume) and then later i permaban him cuz I was smart enough to identify him but not smart enough to stop downloading leaked addons. Well how sad it is, he then talked in console: J'arrive ; this scared me so I stopped my server and deleted some addons.. but still no work.
This happend today btw.

Whats the best way to remove backdoor?
Should I reinstall my gmod and do everything to new? I dont care cuz I didnt start to make jobs and configure addons.

Or should I look in scripts? Thank you for any advices. And as I told my friend yesterday, I don't trust french people when it comes to leaked addons.

ps: pls just help no blame no insults, thus not good for my heart
pss: as u see on my reputation, i have got -2 rep for leaking backdoor addon, tho i was sure that there wasnt any backdoor