Jagex currently investigating.
The worst thing an MMO like RuneScape can deal with is an item duplication hack that goes unchecked. At best it can cause hyperinflation and distrust in the community. At worst it can completely and irreparably tank the game’s economy for years to come. Old School RuneScape is currently trying to prevent such a scenario.
The team at Jagex posted earlier today that they are investigating reports of item duping and people crashing worlds. While there are no plans to do a game-wide rollback, those who take part in the exploit can expect to have their accounts punished for it.
We’re also seeing concerns that generating wealth during this investigation will lead to a game-wide rollback. We have no plans to do this. If we’re able to confirm and verify the reports we will only target the accounts responsible and the wealth and items they have generated. Game-wide rollbacks are always a very last resort and we don’t expect to have to use them in this instance.
Source: Old School RuneScape