For users of the Windows 10 Mobile and Windows 10 Mobile Enterprise, today will mark the last security update. According to the Microsoft support site, Microsoft will no longer support this platform. Creation of new device backups for settings and some applications will continue for three months, ending March 10th, 2020. Some services, such as photo uploads and restoring a device may continue for up to 12 months.
With support for Windows 10 Mobile products being stopped, there is a risk that cybercriminals may take advantage of this by creating malware that targets unpatched vulnerabilities in these devices. However, since Windows Mobile devices were never widely adopted, it is also possible that the platform will not be targeted with malware simply because there are not that many devices to infect. Users of this platform are advised to download and apply this last patch as soon as possible. It is also advised to switch to a supported operating system such as iOS or Android. If a Windows mobile device does get infected, it will become increasingly difficult to remove and defend from new attacks.
Source Article: https://support.microsoft.com/en-us/help/4485197/windows-10-mobile-end-of-support-faq