http://www.fernjager.net/post-8/sdcard:
As a 400 MHz Linux system with 32 MB of RAM, using only ~100 mA @ 3.3 V, the possibilities are endless!
http://haxit.blogspot.com/2013/08/hacking-transcend-wifi-sd-cards.html:
This post is written with the intention of exposing not only the exploits which will allow you to root (or jailbreak) the device, but also the process of discovering and exploiting bugs, some of which are a dead end, while others lead to the holy root B-)
http://hackaday.com/2013/08/12/hacking-transcend-wifi-sd-cards/:
As he suspected that some kind of Linux was running on it, he began to see if he could get a root access on it… and succeeded.