Achivement help, black ops 2

nothing will happen, its a well know modded game plenty have had the achievements that way

You're not going to lose your account, and you shouldn't exactly have anything to worry about.
Stuff like this happens a lot with older games that are susceptible to being hacked. People join lobbies being unaware of what's going on and so long as you're not willingly and therefore acknowledging the fact you joined a modded lobby you should be
okay. A tip in the future would be to not do that ever again and report suspicious activity online using Xbox Live's report features so the people who are cheating are apprehended justly.

There is, however, a minor discontinuity to your story. You said you joined a modded lobby but you also said you couldn't tell if it was modded? Did you join not knowing and then realized it was?

Regardless you should check out these two links for resources about how to responsibly engage in activity online in the future.

https://enforcement.xbox.com/en-US/home/howTo#sub-topic0-0

https://www.xbox.com/en-US/legal/community-standards

Joined then realized it was once those achivements flew in. I was so panicked that i was shaking as i wrote this. Sorry about the confusion

Technically you should not lose your account as it is only a game and a minimum amount in terms of achievements, but remember that it is the ones who manage the game who might find some inconsistency or trap in your data (if so) they are the ones who if
they were s annoy seen yourself in the game or if they think there was an intention to take an advantage

I wouldn't be worried at worst you'd get de-ranked on the game that's all