Preventing unauthorized access to wireless router

Hi guys, thanks for helping out with my other thing a while back.
Though now I’m curious, can Avast protect against users getting past a locked wireless router connection, or is that only an issue with the router itself?
Today I found someone compromised my wireless connection and downloaded something that my phone company was alerted to and suspended my connection.
Needless to say, that was a huge hassle and something I did not want to wake up to. Later they understood it was a misunderstanding working to resolve the issue.
In the mean time I am having them swap out a new router with password while I’m looking at ways to protect myself from this happening.
I don’t know if Avast can detect outside devices connecting to my network, or if a firewall can do that? Or is there other means of protection?

securing router http://lmgtfy.com/?q=how+to+protect+a+wireless+router

http://www.pcworld.com/article/2852252/bitdefender-security-appliance-for-home-networks-seeks-to-replace-endpoint-antivirus.html

it can be placed in front of a router, so that it also protects the router from Internet-based attacks, or can act itself as a router.

Ah! Okay. I’m gonna gonna try to figure out how to do these, the box thing seems pretty cool, but I might have to pass on that. I have a technician coming tomorrow to switch routers and ask them if they can set those up for me.