Shared by cck_my in the forum and also reported by Arstechnica UK, it appears that forum members of the Hardwareluxx.de community found an issue with Skylake using Prime95 workloads. The problem was later confirmed by mathematicians at Great Internet Mersenne Prime Search (GIMPS), the organization behind Prime95. Intel has confirmed the findings and made the following statement to Arstechnica:
"Intel has identified an issue that potentially affects the 6th Gen Intel Core family of products. This issue only occurs under certain complex workload conditions, like those that may be encountered when running applications like Prime95. In those cases, the processor may hang or cause unpredictable system behaviour."
According to Arstechnica, a fix has been developed and will be distributed via the hardware partners via a BIOS update. The bug affects only specific workload scenarios and is not a concern for the majority of the Skylake users. It is confirmed that the issue occurs on both Windows and Linux and can be induces when configuring Prime95 to use Fast Fourier Transforms and an exponent size of 14,942,209.
A couple of sceptic overclockers hinted that this is a way for Intel to lock down the non-K overclocking, but that's not confirmed. Let's wait and see, but even in case the new BIOSes disable non-K overclocking you can still use the currently available versions for overclocking adventures.