Women who constantly surf the net are most at risk of becoming addicted to it.
Researchers have uncovered new evidence of a genetic variant which makes people less likely to be able to tear themselves away from their computers - and the link occurred most frequently in women.
The same genetic variation found to occur frequently in online addicts has already been linked to other forms of addiction - including nicotine addiction - and to loneliness and depression.
His team interviewed 800 people about their internet habits, including how often they thought about it and how much of an impact they felt if they had to go without.
They then looked at the genetic makeup of the 132 who seemed most hooked and compared them to a "healthy" group.
Many of the 132 had the same genetic variant, which was also linked to nicotine addiction.
"What we already know about the nicotinic acetylcholine receptor in the brain is that a mutation on the related gene promotes addictive behavior. It seems this connection is essential for both nicotine and internet addiction," Dr Montag said.
"Within the group of subjects exhibiting problematic internet behavior this variant occurs more frequently - particularly in women." This could be linked to a subgroup using social networks like Facebook," he added.
The study has been published in the Journal of Addiction Medicine.