"After analyzing data collected by a smart meter, these gentlemen were able to determine devices like how many PCs or LCD TVs in a home, what TV program was being watched, and if a DVD movie being played had copyright-protected material. In other words, smart meters do have privacy implications that translate into consumer identification. On the bright side, they showed it takes an amateur hacker only two days to hack a home energy meter and fake the smart meter readings -- which could result in a utility bill showing absolutely no power consumption at all."

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http://www.networkworld.com/community/node/79486