http://www.eweek.com/c/a/Mobile-and-Wireless/Apple-Laptop-Hack-Disables-Batteries-Researcher-to-Show-How-at-Black-Hat-452759/

[...]
Miller examined MacBooks, MacBook Pros and MacBook Airs, and found that many of
the batteries on those units had a 4-byte default password hard-coded on the microchips inside and a second password to give full access to the hardware firmware. With the two default passwords in hand, the perpetrator could rewrite
the chips' firmware. Miller discovered the passwords after analyzing a software
update from 2009 from Apple that addressed an issue with MacBook batteries. He was able to reverse-engineer the chip's firmware and modify the power information it sent to the operating system. He was also able to rewrite the firmware.

The ability to access and send instructions to the chip could be used by other attackers for malicious purposes, such as preloading malware on to the chip, according to Miller. Once the attacker figures out a way to go from the battery
to the operating system, battery-based malware could be used to infect the computer and steal data, take control of the laptop or cause it to crash whenever it was in operation, Miller said.

When faced with this kind of malware, IT administrators and users will wipe the
hard drive, reinstall software and reinstall the BIOS firmware, but not think to check the battery's firmware, according to Miller. "Every time it would reattack and screw you over," Miller said, noting the only way to eradicate or detect it would be by removing the battery.

"These batteries just aren't designed with the idea that people will mess with them," Miller said.
[...]

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