Previously, a number of manufacturers announced the option to overclock K-series Haswell CPUs on non-Z series motherboards, and now Asus has joined in as well.
In the past, typically there were two requirements for overclocking CPUs with the use of a multiplier. You'd need a Z-series chipset on your motherboard as well as a K-series CPU. Now though, it appears that a bug in the 8-series chipsets allows users to overclock Intel Haswell K-series CPUs on non-Z series motherboards, allowing for overclocking on budget motherboards. A K-series CPU is still required though, as non-K series CPUs have an upwards locked frequency multiplier.
Of course, to make use of the feature you need a BIOS update, which can be found on Asus' website. Motherboards that support the feature include the H87-PRO, H87-PLUS, H87M-PRO, H87M-PLUS, H87M-E, H87I-PLUS, B85-PRO, B85-PLUS, B85M-E and B85M-G.