How To: Install a Hidden Backdoor in a Home Router

Very thorough and well written. I'd just like to point out a possible typo or error: "scp nk-mips root@router-ip/tmp"

It should have a colon after the remote host, like this:
scp nk-mips user@host:/dirs/

Just letting you know so as to attract less questions from newbies who don't realise that the command is missing a character.

TRT

Thanks TRT and good catch. It was indeed a typo. I'd had fixed.

I found my ISP router using shodan,and got the password,is it possible to launch a sort of mimt to collect data and crend

First, you have to understand that accessing somebody's else router is illegal.

Said that, high performance routers are different beast and they run special operating systems. Cisco routers use to run IOS (not sure if that is still the case), those seems to be based on QNX , Juniper router uses JunOS based on Free-BSD and, according to the wikipedia page there is an SDK available.

I never had a chance to work with any of those system so I cannot really answer your question. I would suggest you to do some research to find out that is possible.

What If the router is not mine and I don't have access to the control panel?
I want to install a sort-of backdoor to get the password of the network whenever I want. is that possible?