After several years of argument, Ross Anderson of Cambridge University has persuaded his publisher to let him put his book "Security Engineering [1]" online for free download.
The publishers thought for years that it was too risky to let authors put books online but they are gradually learning that this isn't so. Putting a book online often increases its sales; more people read it and those who find it useful often go buy a copy.
Links:
[1] http://www.cl.cam.ac.uk/~rja14/book.html