Digital video recorders have revolutionized home and business security, making it possible to easily store and play back hundreds of hours of surveillance camera footage. But a few design flaws in their software, it seems, can quickly turn the watchers into the watched.Eighteen brands of security camera digital video recorders (DVRs) are vulnerable to an attack that would allow a hacker to remotely gain control of the devices to watch, copy, delete or alter video streams at will, as well as to use the machines as jumping-off points to access other computers behind a company’s firewall, according to tests by two security researchers. And one of