Modern Warfare 3’s month-long Critical Countdown event tasks you with collecting different types of DNA samples across multiplayer, Zombies, and Warzone. We’ll explain how to best collect your DNA samples quickly so you can get your rewards faster.

The best way to quickly collect DNA samples is to play Zombies mode. The risk of dying is very low (but not impossible) and you can easily collect both the Ade and Cyto DNA samples (two of the four DNA samples currently available). Start by clearing the Tier 1 zone and completing contracts such as looting weapon caches and defending areas. This will send hordes of zombies your way, allowing you to get a lot of easy kills early on. Move around the map if you’re more of a roamer or set up a good campsite to take out the zombies. By the end of the contract, you should have collected around 50 kills, which equates to 50 DNA samples.

In general, Cyto (Orange) DNA monsters are much rarer than Ade (Blue) monsters in my experience, so you'll have to farm a bit more efficiently to get them. The most efficient way to get Cyto DNA monsters is by killing special zombies, as they have a higher drop rate. Normal zombies do drop them, but the drop rate is very low (about 1-2 out of every 5 zombies in the Tier 1 zone).

Another way to farm DNA samples is to call the exfil helicopter which will trigger a horde of zombies. When you feel you have farmed enough, you can exfil or use this method again for more DNA samples. Farming in the Tier 1 zone is advantageous because you can easily find a lot of zombies and the risks are also very low. If you farm the Tier 1 zone during the first 45 minutes of a Zombies session, you can easily collect around 1000 DNA samples. This will help you get most of the rewards from the Critical Countdown events.