Afflicted patients cannot find a way to cut back or control their internet use.
Now, preliminary research suggests web addicts have brain changes similar to those hooked on drugs or alcohol.
Experts in China scanned the brain of 17 young web addicts and found disruption in the way their brains were wired up.
The discovery, published in the scientific journal PLoS ONE, could lead to new treatments for addictive behavior.
The research is described as groundbreaking, but larger studies are now needed to confirm the findings.