Attention: THE OLD CHEAT DOES NOT WORK. The programmers fixed the glitch, but this version is a way around the fix :)
(1)-go to a Map or Room and find a Shiny Pokemon. Click "Fight"
(2)-While in battle OPEN A NEW TAB and find a trainer (in a map or room...) with a pokemon in the FIRST SLOT of his party that you want to copy and make shiny. (To make finding people like this easier, I suggest you add anyone you find with good pokemon in their party to your friend's list. When you want to find them, they're there.)
(3)-Go into battle with the trainer
(4)-Go back to the battle with the wild shiny pokemon and hit refresh. (I don't know why, but it needs this.)
(5)-(Do this step all within about 5 seconds) Go back to your battle with the trainer, change your battling pokemon, return to the wild pokemon and hit "refresh" again.
(6)-The target pokemon will appear in place of the wild one, but it wont be shiny yet.
(7)-Close the other Tab (the battle with the trainer) and throw a masterball at your target.
Return to "My Zone". Whatever pokemon you've chosen to steal will be a shiny, so long as the original wild pokemon was also.
(8)-(optional step)INFECT POKEMON INDIGO WITH YOUR NEWFOUND KNOWLEDGE.