Having an affair over the internet is perceived as actual cheating by most people, a survey suggests.
The affairs, even if not physical, are damaging to relationships, the British Psychological Society's annual conference was told.
More than half of 245 students who took part in a survey carried out by Belfast's Queens University said anyone flirting online was being unfaithful.
Experts said they were often a symptom of a relationship in trouble.
Dr Monica Whitty, of Queen's University asked students to complete stories in which one partner in a couple had developed a relationship over the internet.
The stories were then studied to see if the online affair was interpreted as infidelity.
In 51% of cases it was, while 84% of the students thought the other partner would feel betrayed.
Women were more likely than men to see the internet affair as damaging to the real life relationship.
However, some people argued that the interaction was just a friendship or could not be infidelity because no sex was taking place.
Dr Whitty said: "The results of this study show that couples need to be clear what the rules are when it comes to online cheating.
"Emotional involvement, even without physical consummation, can be just as damaging to a relationship.
"It might be easier for people to justify an online affair to themselves, but the consequences, like loss of trust or hurt, can be just as damaging as an offline affair."
Christine Northam, a senior counsellor at relationship guidance experts Relate, agreed there was a danger in internet relationships.
She said they were often a reaction to dissatisfaction in a relationship with one member of the couple thinking they could solve it by having a "fantasy" connection online.
She said: "Up to a point it is OK, but past the boundary is where it is not.
"Where the boundary is depends on the individual relationship."
Rather than resort to internet affairs, people should face up to problems in their relationships by talking to their partner.
If they felt unable to do that alone, they should go to a counsellor, she said.
She added: "Just to bury your head in the sand is not going to solve anything.
"The best thing to do is take your courage in your hands, sit down and have a chat about what you are feeling and what bugs you."
