Apple has issued a voluntary recall order for AC wall plug adapters designed for use in the U.K., Hong Kong, and Singapore. According to Apple, some of these three-wrong adapters are prone to breaking and can pose an electric shock risk.
They were produced by Apple between 2003 and 2010, and included as part of the Apple World Travel Adapter Kit.
In its note to customers, Apple stresses that potentially dangerous units are very rare. So far, Apple has discovered only six incidents worldwide. Considering the millions of Mac and iOS devices sold over that period, this means that only a fraction of a percent of plugs are problematic.
Nonetheless, Apple is doing the responsible thing and recommending that customers return them.
Spotting affected units
These units can be exchanged at Apple Stores and from authorized Apple resellers. More information can be found on an Apple support page.
Apple also provides comparison images so that you can discern between affected devices and newer models. The TL;DR version: Affected three-prong plug adapters are white, with no letters on the inside slot where it attaches to the main Apple power adapter.