To access this mission, open your navigation and pull
. This should open your alerts menu and the first window open should be this tactical alert. Once you choose the mission it will send you to an extermination mission on Earth with level 15-25 enemies. The main enemy will be Scorpions, the female Grineer that uses a melee attack and will pull you to them with a whip. The whip is what the story behind this mission is all about. The Grineer have found a toxin to add to the whip and you are to kill the Scorpions to stop them from using it.
This mission is no different than a normal lvl 15-25 exterminate mission except for the fact that about half of your enemies will be poison whip wielding Scorpions. And let me tell you, if you get in range of these whips they can seriously tear you up. The Scorpions do not always pull you with the whip, sometimes they charge at you making themselves distractions for all the ranged to attack you while you concentrate on them. Properly equipped, you can one-shot a Scorpion on a regular basis, but if they get to you they can return the favor with the poison whip.
I ran this solo and used a ranged tactic. Run into a room and then back up around the corner and pick them off. There were several times when I had several of these enemies coming at me at one time, and my kubrow had to be resurrected several times throughout, but it is very doable. Once you have totaled 50 Scorpion kills, not necessarily in one mission though mine was only one mission, the challenge will pop at the end of the mission. If not in one mission, the total is cumulative.
There is a slight glitch that could happen to you. On my attempt I was glitched into the wall. If you play this game a lot you have probably found yourself inside a pole, wall, or stuck underneath a walkway before, so I was not shocked when this happened. I went to the pause menu and looked at the stats and it said that my mission score was 50. I then aborted the mission as I could not do anything else without burning revives (not to mention the difficulty in suiciding in such a situation) and the challenge popped anyways. So I guess there are ways for the challenge to pop without finishing the entire mission.
Good luck and happy hunting!