Actually it is the most infamous Konami cheat for contra 99 extra lives 2 players can play the game so in a way its multiplayer. But then it was game genie who went beyond any inbuilt cheats or mistakes and then there was all those strategy guides to get certain things that you can't without having one of those guides.
Ahh yes, that's the one I was talking about! Thanks for correcting me, I keep forgetting it was renamed to Contra.
Forgive my stealing the 2 player scenario and using it as an analogy -
1) So in this multi-player environment, if player 1 has 99 lives and not player 2, then player 2 is at a slight disadvantage, yes? Can't remember if there's a continue option, but points-wise, player 2 will have less points since his/her score will probably be reset to 0 if the continue option is used (in UO terms this would be akin to using give arties/resources on a prod shard to save time/resources. maybe the devs accidentally turned it on for a day and player 1 finds out about it)
2) Now, if neither cares about the score and both just want to play it to have a great time, no problems (likewise in UO, there are people that could care less if others cheat)
3) However, what if the score allows you to buy/upgrade to better weapons? In this case player 2 lose out a bit more (in UO terms, player 1 makes tons of scrappers, pendants etc)
4) Both people play the game to have fun, but now player 1 probably feels that he is having more fun. Player 2 probably also feels that player 1 is having more fun, and starts asking, hey, how come player 1 is having more fun than I am because he cheats? (sort of like what people mean regarding cheating having an affect on everyone else)
5) At this point, player 2 may also decide to use the give resources cheat too. At the extreme spectrum, he may feel like not playing further and leaves (people in UO getting sick of the un-even playing field and quits)
Now, let's bring in game genie into the picture -
1) What if player 1 decides to use a 3rd party cheating device, and give himself the ability to move at lightning speed, auto targets and fires at enemies, auto runs to pick up the best powerups once enemies dies. All with 1 single button to toggle the cheat on (speedhacking, automated scripts)
2) Now player 2 feels miserable since he can't compete and decides not to play anymore (certain UO players)
3) Player 1 has no one else to play with him and decides it's not fun anymore (other players)
4) Neither players will continue playing Contra on the NES. They now play Sonic the Hedgehog on Sega
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It has better and newer graphics, but you don't kill people anymore, now you collect rings and kill monsters
5) They now tell other Contra players that Contra was a terrible game
6) Citing that it's NES' fault for not coming up with a way to ensure that game genie not work with Contra. Meanwhile, they are glad that game genie doesn't work with Sega.
7) NES makes drastic infrastructure/design changes to block game genie. Although it costs alot of money, it's very successful. But alot of people likes game genie. A month later, some enterprising gamers release game shark for NES. They have also been making the Sega version of game shark.
8) NES re-looks at this carefully. Should they continue to make the costly changes again that can be circumvented in a couple of weeks? Is it worth the costs to engage in a arms race? Or should they think of a better way? Sue game shark and all future game shark wannabe into submission and stop making it? Buy over gameshark and sell it as an add-on? Should they setup a game shark police squad? Maybe a hotline will do instead? Should they change their policies? What if people don't come back even after all these investments? Should NES advertise this as one of their strengths to entice new players? Maybe add it to their nice spiffy box when they release their new console Super NES Reborn?
Disclaimer - All the above is a figment of my overactive imagination. Any similarities to real life events and/or persons are purely coincidental.
I believe that it's not a losing battle. There are things that can be done to prevent rampant abuse. Some rudimentry ones I have given above, for those demented minds that can fathom what I am actually saying. I am sure that there are many more that the product supplier have thought long and hard about in a much more professional capacity.