A short string of Arabic characters is doing the rounds at the moment. This seemingly innocent string of gibberish will crash apps on your iPhone/iPad/iPod and Mac.
If viewed in your browser, the browser will crash, try to reopen on the same page and crash again (Firefox on the Mac is not affected though).
If someone sends you the code as a text message, your messaging app will recursively crash each time you try to reopen it. The short term fix is to open your address book and flood the sender of the text with "clean" texts. This works by pushing the offending text off the screen.
It may even crash your Wifi.
To date there is no official fix from Apple. They have (reportedly) been aware of the problem for 6 months. They have however fixed the issue in the forthcoming iOS7 and Mavericks.