Are there any online games, specially MMOs, with prohibition for account sharing? And how do they manage it? [closed]

I play a Mu Online server where we used to have a prohibition against people sharing their accounts (so I couldn't login into a friend's account to increase my power in a given event). Recently the admin decided to change the rules and now account sharing is essentially free. As part of his decision, he claimed "no other online game has a prohibition against account sharing and probably because it's impossible to effectively enforce that".

So my question is: is his right? Is it the case that no MMO games such as other Mu Online servers, Tibia, LOL, WOW or any other kind of online video game where someone can play two or more accounts at once have a prohibition against account sharing? And if he is wrong about that, could you please tell me how do they enforce their account sharing prohibition?

In my experience, it is typical that games have some language preventing you from sharing accounts.

Enforcement of that rule is a different story. That would all depend on how much the company sees it as a problem and how much effort they would be willing to put in to combat it. I assume it would also depend on if you're causing other issues by having two accounts (like farming twice as much as a regular person).

So for Tibia, Rule 5a seems to rule out sharing accounts:

Account trading: You are not allowed to sell your own account or to give it away for free.

Account sharing: An account should always be used by one person only. ...Sharing your account data with another person is not only against the rules, but also a high security risk for your account.

For LoL, see Terms of Use item 1.4:

1.4. Can I share or sell my account or login credentials? (No.)

When you create an account with us, we require you to select a unique username and password (collectively, your “Login Credentials”), which you’ll use each time you access the Game. You can’t share your account or Login Credentials with anyone. You can’t sell, transfer or allow any other person to access your account or Login Credentials, or offer to do so. You’re entirely responsible for maintaining the confidentiality of your Login Credentials. Please notify us immediately if you become aware of any breach of security, including any loss, theft or unauthorized disclosure of your Login Credentials.

For WoW, Blizzard has this statement on their Website (though I couldn't actually find these lines in the EULA):

Account Access Limitations

Only you are allowed to access an account registered in your name. We don't recognize the transfer of accounts between individuals. Activities performed on your account are your liability.

You may not share your account or password with anyone, except if you are a parent or guardian, in which case you may permit one minor child to use your account. You may not use your account at the same time, and you are liable for activies conducted by the minor child.

You are responsible for maintaining the confidentiality and the use of your user name and password. You are responsible for all uses of your information, even if you don't authorize them. Security of your account is your responsibility.

As Timmy Jim mentioned in the comments, it's also not allowed on Runescape (as per term 7):

...We grant valid account holders a non-exclusive, non-transferable, personal, limited license, which can be revoked at any time, to use Jagex Products,... You agree to keep your password safe at all times and not to disclose it to any other person. ...

One I'm familiar with from when I was younger was Nexon games having a similar rule.
Their Terms of Use item 2.5 says:

2.5 Account Security.

You are responsible for the confidentiality and use of your account information and agree not to transfer your right to use or access the Service via sharing your username or password to any third person.

So to summarize what I'm getting at, I think that admin was mistaken. Sharing accounts is typically prohibited by the rules or Terms of Service for most online multiplayer games I'm familiar with.