Today in Tech: Yahoo co-founder resigns after having "had enough"

Fortune's curated selection of tech stories from the last 24 hours. Sign up to get the round-up delivered to you each and every day.

* Don't quite follow why some of your favorite Web sites have gone dark today? Here's a tidy explainer of SOPA and PIPA, two anti-piracy bills that could change Internet if passed. (CNNMoney)

* Yahoo co-founder, former CEO and director Jerry Yang resigned from the company because he'd "had enough."  Separately, All Things D also reports that four other board members -- Chairman Roy Bostock, Arthur Kern, Vyomesh Joshi, and Gary Wilson -- may also leave. (All Things D)

* An excerpt from colleague Adam Lashinsky's upcoming book, Inside Apple. (Fortune)

* According to Nielsen, iPhone adoption is on the up and up. Nearly 45% of people surveyed bought an iPhone last December, as opposed to just almost 25% in October. (Nielsen)

* Nokia CEO Stephen Elop on his war for smartphone dominance. (Wired)

* Why failure is just beginning for some startups. (The New York Times)

* Leading textbook rental company Chegg launched a web-based textbook reading app that will allow its 4 million-plus users to look up definitions, ask questions of other users, highlight, and annotate from within the app itself. The announcement comes the same week Apple reportedly plans to unveil a digital textbook service of its own. (Chegg and The Wall Street Journal)

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