Security researchers Abdul Serwadda and Richard Matovu recently tested a pair of EEG authentication systems to see if it was possible to identify personal information from anonymous brainwave scans. The pair created a machine learning system that compared the new brainwaves scans to EEG scans from a group of known alcoholics -- and the machine successfully identified 25-percent of persons who identified themselves as alcoholics in the new sample. "We weren't surprised," Serwadda said of the experiment. "We know the brain signal is so rich in information."

These markers can probably be used to the benefit of medical science, but with brainwave scanners edging closer to the mainstream, it's also possible that the data could be used to identify traits in users. If you're uncomfortable with social networks selling your third-party information now, just think about what it'll be like when they're selling data based on your brainwaves.