I'm going off a Google translation here, so keep that in mind!

Looks like there are a few rotten eggs out there spoiling the fun of Monster Hunter 4. Capcom has posted a notice indicating that some gamers are using unlicensed software/hardware to tamper with save games, gaining access to weapons/armor through cheat methods. Capcom is telling fans that doing this could end up making your game unplayable, and they're also asking online players to keep an eye out for shady activity. On top of all that, anyone caught using this hacked data at Monster Hunter Festa will be removed from all activities at the event.