If you have a Mac running Mountain Lion, I'm sorry to tell you that all it takes to crash almost any app on it is eight little characters.
This strange bug seems to only affect Mountain Lion and doesn't cause your computer any harm. Apparently, it even crashes the error reporter. On its own, the bug doesn't really pose a threat—just don't type it.
But, as a few people have pointed out, it could easily be used as a prank against friends by sending it through iMessage. This will cause the application to just keep restarting itself over and over because it stays in your chat history.
If one of your friends decides to be a jerk, you can easily fix it by clearing out your history. First, you'll have to open up Terminal and make your User Library visible by typing in "sudo chflags nohidden ~/Library/", then pressing return.
Once you've done that, here's how to get rid of your chat history:
- Open up Finder and go to Go -> Go to Folder (or just press Command + Shift + G)
- Enter "~/Library/Messages/" and click Go
- Put all "chat.db" and "chat.db-*" files in the trash
- Empty your trash and restart iMessage
The application should now run normally. Hopefully there's nothing in your chat history that's terribly important, but if you don't want to get rid of the whole thing, you can figure out which file the offending text string is in and just get rid of that one.
Deleting the whole thing is just a much easier option.
Hopefully there will be a fix for this in upcoming versions of the OS, but in the meantime, if you decide to use this trick on any of your friends, at least be kind enough to share this fix with them!