Actually.
I host an open tibia server and I do not use the cipsoft client, my players do. That is their offence not mine.
It is only illegal to
alter the client to suit your game (and offer said altered client for download)
Offer an IP changer on your website
Since the players are responsible for providing their own connection to our "reverse engineered" server emulator we are not legally bound to answer for their actions.
It is however illegal to accept "donations". In order to recieve money for an open tibia server you MUST have a business license. Which is usually quite pricey not worth it unless youre serious.
At any rate Open tibia server EMULATORS are not illegal such as TFS, OTserv. These are seperate works reverse engineered to send the right packets to the tibia client as long as the player has changed the IP.
So, custom client is illegal, IP changers are illegal. (There may also be discrepancies about Gesiors AAC (particularly the images.)
TFS, OTserv are legal.
Now, CIPsoft could narrow it down to the ones who break the above rules and cause quite a stir in the OT community. The fact is OTs are not stable, compared to real tibia, its like free advertising. (IMO)