Lifehacker: “Want to check if a particular internet handle you encountered online (or created yourself) is being used on any other social networks or websites? Sherlock is a free command line application that scans around 400 social networks and finds accounts that match whatever username you type in. Using this service couldn’t be simpler: Just open it up and type “sherlock” followed by the username your want to search for. The program will check every site it can access and tell you where accounts matching your username exist, complete with a link to the relevant profile page. This is useful in two ways: finding people across multiple websites, and checking whether a username you’re thinking of using is already taken on other sites.”