On most and every game I know why do people hack and how?

People hhack using an Action Replay or a Gameshark. The Gameshark was more for the games up to but not including Diamond and Pearl, the Action Replay is used for the Nintendo DS games.

As to why people hack, the only answer I can think of is they want to make the game easier. By hacking they can do almost anything they want. They can get any Pokemon, teach any Pokemon any move, turn evey one of their Pokemon shiny, get any item, make their Pokemon stronger than possible otherwise, and more. The only restrictions are that anything they try to get must be in the programming, which means that they cannot create a new Pokemon nor can they get a Pokemon that did not exist when the game was made (meaning they cannot get a Zorua on Ruby version).

Hacking can severly damage the save file. It can even render the game unplayable. It is a risk that some people do not understand.

Hacked Pokemon are not allowed on to be used in (real world) tournaments and cannot be put up for trade on the GTS (but can be offered on an existing trade). There are ways the game and officials can find hacks, and they often destroy them.

If you get a Pokemon in a trade that you suspect is a hack, it is usually best to delete it (release it) before it can damage anything. Sometimes the checkstops that are ment to find hacks attack legitimate parts of your game as punishment for having a hack.

Personally, I think that hacking takes the fun out of the game. There is no challenge. Finding a shiny isn't exciting, reaching level 100 is no longer an accomplishment.

They use the Action Replay or Action Replay DSi, which are cartradges similar to DS ones.

It can be bought at $20 each, which is much cheaper than Ebay or Craigslist.