Exponents insist it’s not a game – there are no rules.
Rather, it is a “synthetic world” with shops and cars, theatres and estate agents, where you communicate with others via instant messaging or voice.
By way of explanation, Caroline told her daughters that her avatar was like Barbie and her boyfriend was just like Ken, albeit that in this X-rated version Ken happens to own an arsenal of AK47s.
It comes as no surprise, then, to learn that a woman is divorcing her husband after catching him having an online affair.
Amy Pollard, 28, discovered her husband’s character in the arms of another female player – having caught him previously, she claimed, having sex with an online call girl character.
"Sweetie," a campaign from the child exploitation charity Terre des Hommes, is being justifiably rewarded by the creative shows for its effective use of an avatar to catch international paeodophiles.
The project was created by Dutch agency Lemz to combat Webcam Child Sex Tourism - a growing problem in which men from rich countries pay children in poor countries to perform sexual acts in front of webcams.
It may not be real, but a lot of people take it very seriously indeed: both Hillary Clinton and Barack Obama opened campaign offices in this parallel universe.
Companies such as Sony, Ikea, BMW and Coca-Cola also have a presence and Reuters and Sky News have bureaux. But for individuals, a major appeal of Second Life is that it’s like real life, only much much better.
She oozes confidence and pouting sexuality, so it’s no surprise that handsome Keanu Reeves lookalike Nik fell for her. In truth, “Kira” is the alter ego of 33-year-old Kristen Birkin, a dumpy single mother and pub singer from Nuneaton with mousey cropped hair and low self-esteem.
“Nik” is actually Steve Sweet, 47, a mobile phone salesman from Plymouth.
Pollard has made headlines for divorcing her husband, David, 40, on the grounds of “unreasonable behaviour”. Earlier this year, Kristen and Steve appeared on a prescient BBC documentary, Virtual Adultery and Cyberspace Love.
It also featured the extraordinary transatlantic tale of Carolyn, a wife and mother of four from the United States, who became so obsessed with her Second Life relationship that she grew increasingly estranged from both her longsuffering husband, and her angry, confused children.
It’s a world where you don’t have to be dumpy, or from Nuneaton, one where your avatar can look like a model, shop for virtual designer shoes and make virtual friends.