The Factory Reset. One of those last ditch efforts that many of us have a fair bit of experience with. However, a malicious embed code could potentially do the exact same thing to your Galaxy S III. The Unstructured Supplementary Service Data (USSD) code (which we won't reproduce here) apparently only works on Samsung phones running Touchwiz, and only if you are directed to the dodgy destination while inside the stock browser (rather than Chrome, for example). This means the Galaxy Nexus is unaffected, but it can work the same dark magic on the likes of the Galaxy S II.
We've been trying to murder a (UK-based) GS III here at Engadget, but with no luck as yet -- we can cause the malicious digits to appear in the dialer, but we can't force the stock browser to visit them as a URL, even when trying a bit of URL forwarding and QR code trickery. However, this particular GS III has been rooted in the past, even though it's now running an official TouchWiz ROM, and that may be interfering with the process.
Aside from our own experiences, the evidence for the vulnerability is certainly strong. It was demonstrated at the Ekoparty security conference last weekend, during which time presenter Ravi Borgaonkar also showed how a different code could even wipe your SIM card. See the video after the break for the evidence.
Update: Tweakers.net has been able to replicate the security hole on a Galaxy S Advance, while The Verge has confirmed that it works on both the Galaxy S II and the AT&T Galaxy S III. Samsung has told us it's looking into the issue.