Apple has just pushed out a firmware update for the iPhone and iPad which addresses a critical issue with iBooks. Apparently some books were able to open malicious websites and compromise the security of your device. Apple has acknowledged that the new 10.3.2 update remedies URL handling through improved state management and stopped some books from executing arbitrary code with root privileges.
Apple did not disclose whether or not the e-books that were able to launch malicious code stemmed from the iBookstore or if the issue was related to users sideloading EPUB or PDF books from the internet. I believe that the issue was likely from people pirating books from the internet or downloading them through the Safari browser and importing them into iBooks.