"Cybercriminals are taking advantage of the Windows 10 rollout to try and trick unsuspecting netizens into downloading a particularly nasty variant of ransomware,
according to reports.

First reports of the malware came from Cisco Systems Ltd.,’s security team,
which noticed a gang of cybercriminals was stepping up its efforts to spread the CTB-Locker ransomware,
using fake emails that claim to be sent from Microsoft.
The emails tell people their Windows 10 download is ready to install, but that’s actually far from the case."

"Included in the email is a small attachment that is claimed to be a “Windows 10 installer”, but this nasty file actually contains the CTB-Locker ransomware.
Once installed, this nasty bug immediately sets about locking down people’s files, encrypting them so they can no longer be accessed by their owners.
The only way to regain access is to pay a “fine” in Bitcoins over the Tor network within 96 hours,"

Full story: Beware: Stealth ransomware posing as Windows 10 installer | SiliconANGLE