This is a 'trick' question which many applicants won't expect. You need to be prepared for this and should answer it honestly.
If you do not protect your own home as you would a client's network, then suggest to the interviewer the main reason being is that you don't work from home.
"That's a great question and one I've never been asked before. I take my family's security as serious as I do that of the companies I work with. My home network has all the same security measures I recommend to my customers at work. These include a strong firewall, user authentication, access control, and frequent audits. I also upgrade my network hardware, such as routers and NICs periodically as new security features are released."
"Funny you should say that. Many of the practices I recommend to secure a company's network I learned while setting up my personal network. These include using the latest versions of the network hardware and software with the most current virus protection, maintaining a strong firewall, and implementing strong user authentication, or passwords, which are updated frequently. I also monitor the network traffic on my home system to determine if any threats exist. To date, I have discovered many attacks on my system from sources around the world, but so far none of them have been successful at breaching my network."