Most of the hacks were 'fixed', but now they only work if the host is running them so if thats the case you can just leave. But before they 'fixed' it anyone could get infected with these hacks just by simply joining a private match which was running the hacks, then they could use most of them online in any game they played, such as infinite UAV which shows red dots moving in real time and wall hacks, but now you can no longer use these unless you are the host.
When the host is infected everyone in that lobby can use the hacks in that lobby only, so if it's a hacked lobby you will get 1 bullet kills, instant reload, super chopper gunners, care packages are always chopper gunner/EMP etc