Who knows why any particular stock goes up, or down for that matter, on any given day. NQ looks good to me. Recent article at Seeking Alpha, http://seekingalpha.com/article/1126561-nq-mobile-high-growth-strong-tech-dirt-cheap is worth reading.
I think the better question is, why has it been undervalued for so long. Anyhow, the stock looked like it was ready to breakout. We know the floor is around $5 or so with a recent base of around $6. With 2million shares short (13% of float) and $2.7/sh in cash on its books, its a lot easier to move up than down.