Addiction - weakness or Illness

Just listened to the Science Now show on addition.

Lots of evidence that it is an illness not somekind of habit that can be changed by just stopping.
It seems that our brains are good at learning what works for survival. Once we have learned then we are programmed to repeat these things. When something goes wrong we have a need to replete things that do not help with survival (we become addicted), but the need to do them is very strong as it is part of how we are wired. For example under stress we are programmed to go back to going the survival things, which in the case of an addicted person is the addictive behaviors or patterns. The research does seem to support that once something has become an addiction it cannot be enjoyed in moderation and much be cut out entirely.

It would seem that the research suggests that many addictions have a similar root cause.

Question:
What is the difference between an addiction and a like or hobby?