Between wired and wireless security systems, the wired system is less likely to be hacked.
Like all things, if a security system, security camera, or smart home device connects to the internet, it is often possible to hack it. Remember:
"Security is not a product, but a process." - Bruce Schneier, Security Expert (4)
A solid password will help make this less of a problem (5). However, if you Google "how to hack a wired camera" you'll find there's no shortage of results there as well.