The reverse of a string, introduced informally above, can be defined more precisely by the recursive rules ar = a, (wa)r = awr, for all a ∈ σ, w ∈ σ*. use this to prove that (uv)r = vrur, for all u, v ∈ σ+.

Yeah they want to steal your info and sell it on the dark web. they want your credit/debit card numbers, social security numbers, google passwords, and other stuff. some people install spyware onto your device, which, as the word suggests, is built to spy on your every move, such as what you type. they then sell this information to other people secretly or use it for evil purposes themselves. or both, idk. the reason why this info costs money to learn is because its valuable info. im not saying that i condone it though! hacking sucks, and whoever is involved in it is just a horrible person.