Encription of my data files

[REDACTED]

Good evening,
A few days ago (on Dec. 1st) all data files on my PC become at once unaccessible due to the action of some hacker entering in my system even though my Avast antivirus protection was active. A message, whose text is attached here below and explaining exactly what happened, was displayed.
How was all that possible?  Could it be repeated? What have I to do to protect my system from this danger in the future?
Thanks.
Amedeo Donnici

quote
 ________________________1234____________________________________-
What happened to your files ?
All of your files were protected by a strong encryption with RSA-2048.
More information about the encryption keys using RSA-2048 can be found here: http://en.wikipedia.org/wiki/RSA_(cryptosystem)

What does this mean ?
This means that the structure and data within your files have been irrevocably changed, you will not be able to work with them, read them or see them,
it is the same thing as losing them forever, but with our help, you can restore them.

How did this happen ?
Especially for you, on our server was generated the secret key pair RSA-2048 - public and private.
All your files were encrypted with the public key, which has been transferred to your computer via the Internet.
Decrypting of your files is only possible with the help of the private key and decrypt program, which is on our secret server.

What do I do ?
________________________1234____________________________________
Alas, if you do not take the necessary measures for the specified time then the conditions for obtaining the private key will be changed.
If you really value your data, then we suggest you do not waste valuable time searching for other solutions because they do not exist.
________________________1234____________________________________

For more specific instructions, please visit your personal home page, there are a few different addresses pointing to your page below:
1. http://gfhshhf.home7dfg4.com/B2F4BC374541743E
2. http://td63hftt.buwve5ton2.com/B2F4BC374541743E
3. https://tw7kaqthui5ojcez.onion.to/B2F4BC374541743E
 
If for some reasons the addresses are not available, follow these steps:
1. Download and install tor-browser: http://www.torproject.org/projects/torbrowser.html.en
2. After a successful installation, run the browser and wait for initialization.
3. Type in the address bar: tw7kaqthui5ojcez.onion/B2F4BC374541743E
4. Follow the instructions on the site.

IMPORTANT INFORMATION:
Your personal pages:
http://gfhshhf.home7dfg4.com/B2F4BC374541743E
http://td63hftt.buwve5ton2.com/B2F4BC374541743E
https://tw7kaqthui5ojcez.onion.to/B2F4BC374541743E 
Your personal page (using TOR-Browser): tw7kaqthui5ojcez.onion/B2F4BC374541743E
Your personal identification number (if you open the site (or TOR-Browser's) directly): B2F4BC374541743E
-----------------
unquote

[Eddy]

First of all, break the links so no-one can click on them.
We do not want people to visit malicious websites.

Your system is infected with a version of ransomware.
Mostly it gets on a system because the user has opened a malicious mail attachment or installed malware. (could be a PUP).

100% detection at all times is not possible.
Before a cure can be developed the existence of a disease must be known (and also how it works).

If you want help cleaning up your system, follow the instructions :
https://forum.avast.com/index.php?topic=53253.0