I got one legally bought copy of Worms 4: Mayhem. I wonder, if I have others in the house who would like to play LAN with me, can they install the game at their PC and play against me, having installed it from the same CD?

Furthermore, if they play over the internet at the same time as me, will the CD-key get banned?

Not sure about this, but if you run the game, then eject the DVD, the game will continue running, so you can probably install it on several computers and then play LAN.

As for playing over the Internet, if you can run the game, then you can connect, no matter what.

Well the problem is, I know I can run it without the CD. But I also know that most retail games are protected.

Normal games require a CD-key when you start the game, and when you play over the internet. You will then be playing with a CD-key recognised as your unique "ID". That makes it possible to ban that ID if you have done something really bad.

If you have distributed your game to others, like a crack, your game copy will be used by others. In order to prevent that, the company will ban your CD-key if more than 1 of the same CD-key is detected at the same time.
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That's what I worry about. I don't know whether I can let others in the house play the game on their PCs or not, depending on if they will get banned if they accidentally play over internet at the same time as me.

Well the problem is, I know I can run it without the CD. But I also know that most retail games are protected.

Normal games require a CD-key when you start the game, and when you play over the internet. You will then be playing with a CD-key recognised as your unique "ID". That makes it possible to ban that ID if you have done something really bad.

If you have distributed your game to others, like a crack, your game copy will be used by others. In order to prevent that, the company will ban your CD-key if more than 1 of the same CD-key is detected at the same time.
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That's what I worry about. I don't know whether I can let others in the house play the game on their PCs or not, depending on if they will get banned if they accidentally play over internet at the same time as me.

Just try it; what have you got to lose? Besides, Starforce only checks against the CD to make sure the CD itself isn't a copy; it doesn't use the internet as I was able to register W4:M offline.