1. Interactive Advertising Bureau.
http://www.iab.net
2. Internet Live Stats (2015).
http://www.internetlivestats.com/total-number-of-websites
3. Online advertising (2015).
https://en.wikipedia.org/wiki/Online advertising
4. Right Media (2015).
https://en.wikipedia.org/wiki/Right_Media
5. Adler, M., Gibbons, P.B., Matias, Y.: Scheduling space-sharing for internet advertising. J. Sched. 5(2), 103–119 (2002)