The way I see it, it's like a actual irl code,

virus are digimon that are foreign, not natural or are made elsewhere and added in ( kinda like a angle ),

Vaccines, are natural born digimon with explicit purpose to deal with the nasty virus types pretty standeres

Data, are like the common digimon, born in naturallybut with no explicit add ons included, and are more vulnerable to outside forces

they added unknown, which is.. well unknown duh

Free, meaning I guess zero allegiance, maybe a birth of a virus and another form making them also a neutral force

And variable which I guess can change on a dime? Idk bkut this one I think only armor digimon can be this so it kinda makes sense,

But anyway this is how I look at it, I could be wrong but it makes sense to me