There is an ongoing malware / ransomware all over the world called wannacry right now. From what I can gather, the malware exploit a vulnerability in windows smb remote execution code (smb = file and printer sharing) to spread the malware. It then will search for documents, encrypt it and ask for money for decryption. News said the ransom started at $300 and raised up to $600.

Windows that's affected by this are XP up to 8. Not sure about 10, but it looks like 10 doesn't have this vulnerability. Microsoft has provided patch for this. Yes, including windows XP gets it. Windows users are strongly advised to install the update.