According to Microsoft, the support cycle for both Windows Phone 7.8 and Windows Phone 8 ends in 2014. This pretty much means that those who run either of these two operating systems on their handset will no longer see security updates after 2014.
Mainstream support for Windows Phone 7.8 ends 9/9/2014, while mainstream support for Windows Phone 8 ends 7/8/2014. "Microsoft will make updates available for the Operating System on your phone, including security updates, for a period of 18 months after the lifecycle start date. Distribution of the updates may be controlled by the mobile operator or the phone manufacturer from which you purchased your phone. Update availability will also vary by country, region, and hardware capabilities," Microsoft explained. By the time it is 2014, we should see a newer Windows Phone operating system, which will begin a whole new support cycle. Rumors are even suggesting that Windows Phone 7.8 is the last operating system to support legacy hardware, so we will have to see whats in store from Microsoft as this year progresses.