Microsoft Defender Antivirus detects and removes this threat. 

Ransom:Win32/LockScreen.BO is a threat that displays an image across your entire screen, preventing you from accessing your desktop. It tells you that to regain access, you must buy an online voucher to send to someone online. This type of threat is called ransomware, as it asks for a ransom, or fine, for you to regain your property.

Our ransomware FAQ page has more information on this type of threat.

The trend towards increasingly sophisticated malware behavior, highlighted by the use of exploits and other attack vectors, makes older platforms so much more susceptible to ransomware attacks. From June to November 2017, Windows 7 devices were 3.4 times more likely to encounter ransomware compared to Windows 10 devices.

Read our latest report: A worthy upgrade: Next-gen security on Windows 10 proves resilient against ransomware outbreaks in 2017.