I don't believe it's malicious—the "handshake" is just the device requesting that the USB port switch to high-power mode. The line is always 5V, but the device needs to request to draw anything more than 0.1A.
In the case of wall-transformers for iPods, phones, etc, they're either using an unstandardized handshake (such as the phone shorting its two data lines, which can be recognized by the transformer with just a relay), or they provide power all the time, which could damage a low-power device that was inadvertently plugged in.
In the case of wall-transformers for iPods, phones, etc, they're either using an unstandardized handshake (such as the phone shorting its two data lines, which can be recognized by the transformer with just a relay), or they provide power all the time, which could damage a low-power device that was inadvertently plugged in.