The study has two arms and are conducted in Norwegian. Users who registered with a new username on www.slutta.no, after study start May 12th 2010 and before November 1st 2012, are eligible. All phases of the trial, from randomization and informed consent procedures to data collection, are automated and conducted online. The following inclusion criteria are used: age 16 years or older, access to a mobile phone with a Norwegian phone number and they must submit an informed consent form.