Using Tor, or The Onion Router, enables users to hide their online activities. Advocates say the network protects the privacy of activists. But prosecutors say it's used extensively by criminals — and is making it harder for law enforcement to do its job. Daniel Acker/Bloomberg via Getty Images hide caption

itoggle caption Daniel Acker/Bloomberg via Getty Images

The four undergrads of the Diaspora team were given "a global commission to rebottle the genie of personal privacy" after scoring $200,000 in a Kickstarter campaign and support and mentorship from Silicon Valley's brightest. Henrik Moltke/Flickr hide caption

itoggle caption Henrik Moltke/Flickr

A Google data center in Council Bluffs, Iowa. Even online privacy advocates acknowledge that keeping personal data out of the hands of third parties is virtually impossible today. Connie Zhou/AP hide caption

itoggle caption Connie Zhou/AP

A promotional image from Renew shows one of its recycling/advertising kiosks in London. City officials asked the company to stop recording data about the phones of passing pedestrians. Renew hide caption

itoggle caption Renew