Decades went by since Mark Weiser published his influential work on how a computer of the 21st century would look like. Over the years, some of the UbiComp features presented in that paper have been gradually adopted by industry players in the technology market. While this technological evolution resulted in many benefits to our society, it has also posed, along the way, countless challenges that we have yet to surpass. In this paper, we address major challenges from two areas that most afflict the UbiComp revolution: security and privacy. We examine open problems on software protection, long-term security, cryptography engineering, and privacy implications. We also point out promising directions towards the solutions of those problems. We claim that if we get all this right, we will turn the science fiction of UbiComp into science fact.