A massive multiplayer game (MMO) runs primarily on very powerful servers that live in the internet cloud. This is obviously essential so that all the interaction between players and with the game itself can take place. However a lot of the game also runs on the player’s computer, the software that does this is known as the client. In traditional boxed MMOs the client is quite big and comes on a disk when you buy the game, or as a big download.
A lot of more recent MMOs are so called browser games, because they work inside your Windows Explorer, Firefox or other web browser. Some people, very mistakenly, think that this makes these games safe. It does not. When you play the game you are letting it download client software into your computer without you knowing. And once that software is in your computer it can do anything it wants and it can download new software into your machine any time it wants without you knowing. And because you chose to download the client in the first place (by playing the game) your anti virus and anti malware protection software will see nothing.
So what could malignant client software do in your machine? Well it could log your keystrokes and send your credit card details back to its operators. You wouldn’t know this had happened until your credit card was robbed. And obviously it would know all your passwords. Another thing it could do is to access and use all your contacts, in your email, your facebook and so on. Then it could use these contacts for spamming or for spreading a virus or for lots of other purposes. Yet another thing the client software could do is to work as a trojan, taking over your computer and using it for all sorts of illegal activities. As you can see the potential downside is massive.
Now you are going to tell me that the same applies to any game. It does and there have been instances of viruses in boxed games. So basically, every time you play a game on your computer you are entering into a pact of trust with the provider of that game not to abuse their position by putting naughty software on your machine. Obviously with big, established publishers there is no problem, they have their reputations to protect and it would be commercial suicide for them to do anything wrong. So they can be trusted. However when a game company comes from nowhere and doesn’t even have an address or a phone number you are taking a massive, an enormous risk.
You can see how attractive this is for someone who intends harm. They can put a game out and very easily gain control of millions of computers. Because game players are ignorant about the client software being put on their machines. This could even be used as a weapon by a hostile government.
Finally, for some well established MMOs, it is possible to download alternative clients into your computer that have not been written by the game’s publisher. These alternative clients are engineered to do part of the game playing for you, to enable you to cheat. Once again you need to be very, very careful of these because they are not coming from the proper game publisher. So they can put anything they want inside your computer.