Malicious software is nothing new. Viruses have been created and spread since before physical networks became popular; back then viruses spread via floppy disk and modem connections with shared systems. Viruses weren't so rampant and protecting your data was relatively easy before networks became popular.
Today, viruses are far more sophisticated and methods of spread have changed making it easier to be infected. This article is specifically about ransomware - for more information about viruses and malware, see my article about using the internet safely
Unlike viruses and spyware, which simply attempt to steal and destroy your information, ransomware goes to the next level. Typical ransomware will encrypt your data and then demand money with the promise to allow you access to your data again; like the name implies.
If you don't pay the ransom, you can expect to never see your data again. Be aware that paying the ransom doesn't guarantee access to your data either. In some cases, even after the fee is paid, not only will the scammer not unlock the computer, but they might use the credit card information to gain more money by charging more to it or distributing it to other scammers.
Sadly there is another method of infection not mentioned in my internet safety article. This method relies solely on social engineering and the telephone; okay and some internet too.
I personally have received a number of these unsolicited phone calls from "Technical Support" telling me that my computer is "sending errors" to them or "sending viruses" to the internet. These callers are relentless. They will push and try to trick their victims into giving them remote control of a computer or installing "diagnostic software" which is actually malicious software.
Once the scammer gains control of the victim's computer, the possibilities of the damage they can cause is endless. They can install more malicious software, spamming utilities, steal your data, empty your bank account, distribute private content and more.
Apple, Microsoft, HP, Dell, Symantec or any other hardware or software provider will not send you an e-mail or call your telephone to advise you that there is a problem on your computer. If you reach out to them for support first, they will likely respond, but they will never contact you first. Ignoring the costs of monitoring/diagnosing every installed device, there are privacy implications there.
Protect yourself; don't install their software and don't let them gain control of your computer.