Target Co. estimates that at least 70 million individuals may have had information including their "names, mailing addresses, phone numbers or email addresses" stolen in a recent data breach. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images

The logo and a page of mobile app "Snapchat" are displayed on tablets. Hackers broke into Snapchat, the popular mobile app, accessing the phone numbers and usernames of 4.6 million users and publishing them online. Lionel Bonaventure/AFP/Getty Images hide caption

itoggle caption Lionel Bonaventure/AFP/Getty Images

The Toyota Prius, seen here at the New York International Auto Show in March, was one of the cars security experts Chris Valasek and Charlie Miller showed to be susceptible to attacks by hackers. Mike Segar /Reuters /Landov hide caption

itoggle caption Mike Segar /Reuters /Landov

An image of the site promoting Def Con 21, a large annual gathering of hackers in Las Vegas. The meeting's leader is asking federal workers to stay away from this year's event. Def Con hide caption

itoggle caption Def Con

After high-profile accounts have been attacked — including AP's, NPR's and the BBC's — Twitter considers how to thwart hackers and protect users. iStockphoto.com hide caption

itoggle caption iStockphoto.com

This 12-story building houses a Chinese military unit allegedly behind dozens of cyberattacks on U.S. and other Western companies. It's in a modern, if bland, part of Shanghai. Peter Parks/AFP/Getty Images hide caption

itoggle caption Peter Parks/AFP/Getty Images