Old School RuneScape has been taken down indefinitely due to "an issue affecting the game" that came after the most recent update was deployed. From collected Reddit threads, it appears that items were turning into stacks of coins, the in-game currency. Each stack, according to users, contained the maximum number of coins possible for them to have: In other words, 2,147,483,647. Every item on every kill was being transmuted into similar-sized stacks.
That, in and of itself, is bad enough, but as PCGamesN noted:
The problem is Old School Bonds. The basic version of OSRS is free-to-play, but most of its content - such as most of its skills and quests - is members-only. You can pay for membership with real money, but also with in-game gold via Old School Bonds. Bond prices fluctuate, but generally they cost a hell of a lot... unless, of course, there's a bug that gives you practically unlimited gold. This Reddit comment suggests that players did indeed catch on and "redeemed bonds with the money" they got from the bug, concluding, emotively: "OMEGALUL." Omegalul, indeed.
From the Old School RuneScape team:
Old School RuneScape is offline whilst we investigate an issue affecting the game.
We're very sorry for any inconvenience caused, and we will restore service as soon as possible. We will endeavour to restore the game to its state prior to the emergence of the affecting issue.
We don't yet have an estimated time for resolution.
Thank you for your patience, and we'll continue to keep you updated.
Update: 14:20. There's still no estimated time for resolution, though we're preparing the essential work needed to restore the game as detailed above. Again, apologies for any inconvenience and thank you for your patience.
Update: 15:10. The work required to bring about restoring the game (a rollback) is now commencing. There's no ETA as to its completion.
The Old School Team
Read more about the issue in this Reddit thread.