The difference between internet porn and porn from the past is just the abundance of new material that there is. Each time you view something new, your brain gives a hit of dopamine. In fact, porn addicts are not really addicted to porn, they're addicted to the chemical sensations that their brain provides. At the basic level, it really is not much different from any other addiction. Old, offline porn is different in that it gets stale pretty quickly. There are only so many times you can look at a magazine or video without it getting boring.
The problem with this is that your dopamine levels get out of whack. You need a higher and higher amount to feel satisfied. This is how people get roped in. This also caused normal, life things that were once enjoyable to become less so, such as hanging out with friends or programming. Life just becomes more dull. In fact, now that I have learned about this, whenever I see a post on HN about how someone has lost their interest in programming or other activities, the first thing I think of is probably this person has a porn addiction. It's not a far stretch seeing as how most of HN is young men. Having drastically reduced the amount I see, I have noticed many benefits in my life including better health and ability to focus better.
Porn, like other addictions, are also a way of masking stress and a way of distracting yourself from negative emotions. Dr. Gabor Mate has done great research linking addictions of any kind to stresses in the body. Porn gives a way to temporarily release the stress but puts the person in a vicious cycle of causing more long-term stress.
Personally, I use the recovery information from http://www.feedtherightwolf.org. It has been the only thing I have across which can really break the cycle.
As someone else pointed out the videos from http://yourbrainonporn.com/your-brain-on-porn-series will really help you understand what is going on in your brain.