Thanks mate!
What type of information can you see about a player?
Only the IP of the router?
Possible to have a log and see the 5 past IPs connected to an account?
Yes it is, but for example, a lot of players use VPNs to connect to OTServers to reduce lag. Such as PingZapper. Some of these players (if not all) will have the same IP Address when connecting to your server.
So lets say you log everyone's last 5 IP Addresses. It may look like 25% of your server are MCing or Sharing accounts or something, but they are actually just using PingZapper, WTFast, or ReduceTheLag.
Plus, people who are "good" at MCing, just use Virtual Machines, which look like completely separate computers. And not only that, they can mask their IP Address and make it look like they are all coming from different areas.
The best it would do, would be an additional took you could use to investigate, but you'd never be able to use it as a accurate system to determine who is MCing multiple characters.
If you used the OTClient, you could give each client a unique ID when it firsts connects to the server. But as soon as players find out about it, they will just install the client multiple times. And all your hard work will do nothing to stop players from using MC.
Your best bet is to make it so even if someone uses MCs, it is not very profitable. You can look to Xagul's Deathzot for inspiration on this. He made a ton of different systems to give players who are actually playing the game, and not botting an advantage. Yes, people still use MCs, but it is less effective than a normal player.