There are actually different ways to look at this situation for the hard reset.
But first, if it was TDL3, then this has been happening since mid-July. I am helping a user defeat this current issue, and have been helping him since early-mid July. He got this infection back in early July.
The infection has two ways of entry... default admin password for router, or it can install a keylogger and if the user logs in to their router using their password, the infection can grab the password and use it in the future to hack in to the router.
Now, on to the hard resets.
(1) Holding the reset button down for 30 seconds is a hard reset. This will only reset the IP address, and reset the password and a few other simple settings. However, this will NOT reset the firmware.
(The non-factory variables in the firmware will still be there)
(2) 30/30/30 reset: Hold the reset button down for 30 seconds, unplug the router, and keep the reset button down for 30 more seconds. Then, plug the router back in, keeping the reset button down for 30 more seconds. This should fully clear the nvram on the router, and reset the firmware.
If the 30/30/30 reset does not work the first time, it may have to be done once or twice more to make sure the reset occurred properly.
Note: if you want to try a cold boot for the router... it will require 30 seconds for the power to be off on the router. After any reset for the above, a password for the router will be reset to admin. The password will need to be customized for security purposes.
Jay
seCURE Connexion Consultant