Anyone with a brain would know it's illegal, just like anyone would know selling weed is illegal unless you own a dispensary, and can get a really harsh sentence.
Sure, but selling weed generally doesn't harm anyone, while sabotaging and extorting a company directly causes harm to its owners, employees, shareholders, and customers. Not to mention the harm caused by infecting millions of people's devices to create the botnet in the first place.
- G.K. Chesterton