This is a brand new illusion called the Scintillating Grid illusion. It is similiar to the Hermann Grid illusion, yet much more powerful in its effect.

     Although the Hermann Grid illusion is pretty well understood, where the effect is due to lateral inhibition, the Scintillating Grid illusion, is much more complex. This Scintillating Grid illusion is distinct from the Hermann Grid illusion in that eye movements are important. Although there was a pretty comprehensive article on this illusion in Vision Research, the underlying mechanism behind it is not yet fully understood.