Ransomware? Software that asks for ransom?

I am no security expert.

I have heard of the wide spread of ransomware. It may work like this:

1. Delete all your back up files. (Dangerous)
2. Encrypt the rest of the files without you knowing it. (Disastrous)
3. Ask for your money to decrypt the files. (Horrible)

What can be done before all the bad things happen?

1. Back up your data to an offline disk. When saving data offline, the chance of being attacked on the Internet is 0.
2. Install the firewall, antivirus and operating system properly. Update the software as new vulnerabilities are detected.
3. Do not run or open suspicious emails and files.

What can be done to decrypt the encrypted files?

1. Contact the security software companies.
2. Decryption may be possible. 
3. Decryption may be impossible.