Some of Apple's AC adapters have been found "in very rare cases" to break and then cause electrical shock when touched. Consequently, they've recalled them and offered up a free exchange program.
The adapters in question are two prong devices intended to be used in Continental Europe, Australia, New Zealand, Korea, Argentina and Brazil. They shipped with Macs, some iOS devices, and the Apple World Travel Adapter Kit. Adapters with a 4 or 5 characters or no characters on the inside slot where it attached to an Apple power adapter are affected, whereas those with a country code are not, as seen in the image below.
For further help on identifying if yours is affected, hit the source. There you can also set up a refund.
