Yesterday, there was speculation it was due to China [1], increased legitimacy [1], or a ponzi scheme [2].

A few comments here: https://news.ycombinator.com/item?id=10497141

[1] http://www.bloomberg.com/news/articles/2015-11-02/bitcoin-is...

[2] http://www.dailytradingprofits.com/5063/is-bitcoin-being-pum...