Web cams have gotten a bad reputation for being insecure. This reputation is somewhat deserved. Lots of them included back door accounts that were hardcoded and allowed anyone knowing the password to access any camera. In fact, you can still find sites online that index insecure cameras, and there are lots of them.
So, should you stop using these old cameras? You don't want anyone to be able to access your video, and even if you don't care about people seeing your camera's feed, it could eat up your bandwidth.
Luckily there's an easy fix. Rather than put your camera right on the internet via port forwarding, you can leave port forwarding disabled and use a VPN. Without port forwarding, normally your camera would only be accessible from within your LAN. When setting up a VPN, you need an extra layer of security and encryption to access devices on your LAN.
VPN setup can be complicated, but luckily, many modern routers support it out of the box. iOS devices can connect to many VPN servers without additional software, and one of the most popular VPN types, OpenVPN is accessible from iOS devices using a free app.
How-to-Geek has an excellent article on setting up your own VPN. If you use web accessible cameras at your home, I'd suggest checking it out!