focus() behavior can be used to inject or steal keystrokes — Mozilla

Google security researcher Michal Zalewski reported that focus could be used to change a user's cursor focus while they are typing, potentially directing their keyboard input to an unintended location. This behavior was also present across origins when content from one domain was embedded within...

CVE-2010-1184: Undefined Security Weakness

The Microsoft wireless keyboard uses XOR encryption with a key derived from the MAC address, which makes it easier for remote attackers to obtain keystroke information and inject arbitrary commands via a nearby wireless device, as demonstrated by Keykeriki 2...

CVE-2007-4693: Improper Authentication

The SecurityAgent component in Mac OS X 10.4 through 10.4.10 allows attackers with physical access to bypass the authentication dialog of the screen saver and send keystrokes to a process, related to "handling of keyboard focus between secure text fields."...