who exactly issued this warning?
You should back your files up anyway - you certainly could lose everything if your computer crashed. Buy an external hard drive, plug it in, copy your files over to it, then unplug it and put it away somewhere safe. Repeat as necessary.
You do also need some sort of computer security. Your system probably has a firewall already. In addition you could sign up for a free antivirus programe like Avast and probably Malwarebytes as well (also free, and you should run a scan with it every week or two). But you don't need to enter paid contracts; free programmes are just as good.