It is reasonable and possible to program these games in such a way that the client is assumed to be malicious, but this is not a common practice. Preventing ch

It is reasonable and possible to program these games in such a way that the client is assumed to be malicious, but this is not a common practice. Preventing cheating would be possible in the general case. For most existing games, though, a modified client already enables the user to cheat. It is just more difficult to create it without the source.