Wednesday 3 February 2010 11.40am
The scientists spent many hours on the internet before coming up with these findings.
Internet use linked to depression
A "dark side" to the internet suggests a strong link between time spent surfing the web and depression, say psychologists.
British scientists found that the longer people spent online, the less likely they were to be happy.
A small group of the worst affected individuals were both depressed and addicted.
But it was not clear whether using the internet causes mental health problems, or whether people with mental health problems are drawn to the internet.