This year was no different. Big hacks hit a range of high-profile targets, from the web's leading adultery website to the federal Office of Personal Management. We're also ending 2015 with a doozy of a hack mystery: Juniper Networks discovered two unauthorized backdoors in its NetScreen firewalls, one of which would allow the unknown hackers to decrypt protected traffic passing through the firm's VPN/firewall.

Juniper Networks found the backdoors at an apropos time—US officials are aggressively pressing US tech companies to install backdoors in their systems to let the government access protected communications for criminal and terrorist investigations. But opponents have long argued that a backdoor for the government would create a vulnerability that bad guys could exploit as well.