A team of Princeton and Harvard researchers analyzed the phone call records of 15 million users in Kenya -- not to spy on people, but to study the spread of seasonal disease. The team wanted to see if the movement of phone users can predict outbreaks of seasonal diseases like rubella or German measles. So, they used anonymous records from between June 2008 and June 2009, including locations where people made phone calls. They then compared the data to the areas where cases of rubella were reported in the country. The result? Well, it turns out the subjects' movement patterns matched the locations with the highest risk of rubella within that year-long period.