Read this on twitter this morning: "the USSD code to factory data reset a Galaxy S3 is..." and "this will hard reset the phone, no user confirmation needed." It's been reported by Droid Life and others. I'm not interested in sourcing this to figure out who to credit for the uncovering this and obviously I'm leaving out the specific code from the tweet (go find it yourself if you care too).
Entering the code will reset MANY/MOST of Samsung's current phones (including S3). It can be activiated via HTML on CERTAIN phones (e.g. d2att is reported right now). What does this mean? A malicious user could reset your phone by tricking you into clicking a link, QR code, or NFC. Will this be patched? I'm sure at some point.
As far as I can tell, this affects stock and TW roms only. AOSP phones are not reported to have this flaw. I will test later tonight when I get my internal SD card pictures and movies moved off. I'm sure most folks would be inconvienced at worst, but some folks could really suffer from an uninteded reset.
My advice, don't panic, back your stuff up, and proceede with caution. I doubt many malicious sites will crop up just to slay the S3, but you know those apple fanboys (kidding). I'll update with info when I can try it on my phone.
Edit: Some users have reported this as an old issue. It is not. I just performed the reset by entering the USSD code on a stock, updated phone. It wipes your data and cache, but not your internal SD card for those wondering. Your custom recovery is also left in tact.
Edit 2: You can type *2767*3855# in your dialer and it WILL reset your phone without asking you to confirm. This happens on stock d2vzw and beans 11. I can't determine if this can be invoked by inserting this string into html code. I tried to insert it into the frame source myself, but couldn't make it happen. Then again, I'm only a casual html programmer so this proves/disproves nothing. If it's not been patched for your phone, then a person could make a web page w/ the code and then just send you a wap push sms and you are reset.
Folks, read up if you care to. Probably much to do about nothing, but back to AOKP I go. Just trying to help