Bootleg Operator Achievement
Collect all Bootleg Zombrex
There are five of these you need to collect in each zone for a total of 20. They become available to collect after returning the first Zombrex (not part of the forty) to Cora back at the hospital. They are marked on your map by a yellow circle with a + icon inside which will show up when you are fairly close to them. The best time to collect these is while you are waiting for Nelson, alongside the other collectibles.