Virus farming is a tactic you can use to obtain massive amounts of mass when you have a small amount of mass. It functions in some servers, namely Splitrun Paradise. The tactic works best when you have a teammate and around 5k-15k mass. Before we go any further, we must learn how to shoot a virus. you can shoot a virus by ejecting mass at it, it will grow bigger and bigger, and then another virus will shoot from it in the direction which you ejecting mass into it. This tactic is useful in fights where you and another person are locked in a battle, at 3k-20k mass, and since nobody is bigger that the other person, you or your teammate shoots a virus at the person who you are fighting. When the Virus enters their cell, it divides it into many smaller particles, which will allow you to split at the and eat them, or if you were nearly on top of them, you will absorb them.
Now that we know how to shoot viruses, we can learn how to virus farm. The point of virus farming is to gain large amounts of mass without having to engage in battle. To start, gain at least 5k mass. Then, go somewhere on the edge of the server, and shoot a bunch of viruses and the edge, it will work faster if you split at a virus and then begin ejecting. Keep shooting viruses until you have around 2.5k mass left. Then, split at one of the viruses, then split again. This will result in one much bigger cell emerging where the viruses were, and with many smaller particles around in, which you should condense into your cell or feed to your teammate.
Now, let me explain why this works. The first thing to understand is the max particle limit. There is a certain number of particles you are allowed to have, and if you reach that limit, then nothing, not even a virus, namely, can reduce your cells into more particles. When you split at the virus the first time, after shooting them, it gets you halfway to the max particle limit. then, when you split the second time, you will have reached the limit, and the cell, which was just sent into the viruses, will absorb all of them and become massive.
I hope this helps :)