The first firmware updates to fix a security issue have been issued for the popular Asus routers, with the top of the range Asus RT-AC68U getting a new release of firmware that can be downloaded from the Asus support website.
The security issue was that when people connected a USB HDD or thumb-drive the default FTP access did not require a password. The new firmware will default to requiring a password to be defined, or if people really want to let the world access their files they can opt for unlimited access. The problem affects other routers in the Asus RT range, including the RT-AC56U, RT-AC66U, RT-N66U and RT-N16 and firmware updates are expected in due course.
https://www.asus.com/Networking/RTAC68U/#support
http://www.thinkbroadband.com/news/6229-new-asus-router-firmware-to-fix-ftp-security-issue.html