It's like 1999 - Patch, AV and Backup
Who remembers Melissa and the ILOVEYOU attacks?
And nearly 20 years later, the patch, AV and backup advice is as relevant as ever. Some things have changed; 20 years ago, we'd get an infection, we'd submit the file (or link) to our AV vendor and they'd send us an update. Today's AV can be a bit more clever, it will detect some types of malware/ransomware/viruses without a specific patch.
It's surprising that even now, the basics of patching aren't followed. We have a "patch Tuesday" when we know patches will be released from Microsoft. They also provide a patching service built into Windows Server so in effect this is a no cost option and is fairly straightforward to set up and maintain.
If you haven't been infected, good news. You can do a lot to prevent being infected, but as we see, even the biggest businesses can be caught out. Stay vigilent.