Extra help to block ransomware (no disk encryption unless keyboard OK)

The Sunday NY Times Week in Review (Jan 4, 2015) had an article about someone’s mother having to pay Bitcoin ransom in a ransom malware encryption attack.

At home, what should I do to prevent a ransom encryption attack, in addition to Avast AV (on my home Win 7 Pro 64-bit and my home XP Pro SP3) or Windows Defender (on my home Win 8.1 Pro 64-bit)?

One of the readers asked whether there’s an app that prevents encryption of a disk or partition unless there’s confirmation at the keyboard (like a UAC prompt). Sounds like a good idea - is there any way for me to add this?

Thanks.

(PS and FYI – I have Windows Defender on my 8.1 because Avast 2015 uses up the entire capacity for hardware-assisted virtualization, which I intend to play with later. Similarly, on my 7, I still have Avast 2015 but I have turned off its “Enable hardware-assisted virtualization” for the same reason. Finally, on my XP, I have Avast 2015 and have left ON its “Enable hardware-assisted virtualization” because, on XP, there’s no interference with HAV. But probably not relevant to my question.)

Step one is to make a backup of all important data.