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

An analyst works at a federal cybersecurity center in Idaho in 2011. Experts say Internet-connected infrastructure is a possible target of cyberwarfare. Mark J. Terrill/AP hide caption

itoggle caption Mark J. Terrill/AP

Cyberattack headquarters? The 12-story building in a Shanghai suburb that American investigators say houses an operation responsible for hundreds of cyberattacks on companies around the world. Peter Parks /AFP/Getty Images hide caption

itoggle caption Peter Parks /AFP/Getty Images