Although home computers were first tought to be expensive tools, people have always used them to have fun. Especially many youngsters since the 80's have had a computer and computers have become a hobby for many of them. As in real life, friends form teams and groups to play games and to compete, friends in computer world have formed groups to have fun, to appear under the same name and to compete with other groups.
These groups are usually categorized based on what they do. Nowadays the categories are roughly the following: demo groups, cracking groups and couriering groups.
The name "demo group" is pretty much self explaining. Demo groups compete with other demo groups by releasing demos. They try to make the demos look as good as possible and they usually try to do something new, something they could be remembered of. The base of every good demo group are coders, the freaks who program demos. It is mostly depending on their skills, if the groups is going to be successful. But even when the group has skillful coders the success is not guaranteed. The demos should look good and they should be original. This is where good graphic artists are needed. In many cases the coders are more technically oriented and do not possess very good skills in designing the demos or drawing the graphics. So it is the job of graphician to judge what the demo should look like and to create the graphics needed. In addition to these, demos need music and sound effects. Creating the music is the job of musician. Like the coder and the graphician, musician can make the difference.
Cracking groups are the second major category of computer groups. Their activities center around the illegal side of computing, piratism. What they do is basically getting the latest software as quickly as it is released (or often even before it is released), cracking it and then distributing the cracked version. The glory builds up as the group becomes known for fast and working releases. As soon as there were commercial programs sold for home computers, there were crackers. One could say that crackers have always existed in computer scene.
Closely related with crackers are traders or couriers. They are people who "trade" the cracked programs (or "wares" as the slang term goes). In the 90's trend seems to be that the cracking teams do the cracking and those who do the trading have found their own groups. These are known as courier groups. The software, they distribute nowadays mainly over the internet, is usually cracked the same day or the day before. In the 80's wares were traded (or swapped as it was called) by nearly everybody involved in the computer scene. In those days the job was done via normal mail.
In addition to these, there are other smaller categories; those groups of which it is difficult to say, how they should be categorized. But let's mention music groups. There are not many of them, but they surely exist. Often they are formed of musicians who are members of different demo groups, but who want also to release just music together with their fellow musicians.