By Rory Cellan-Jones
Technology Correspondent, BBC News
Is Stephen Fry really on Facebook?
As Facebook continues its explosive growth here's one question troubling me. Are my friends for real?
This week I received this intriguing message from a man who moves in London's new media circles.
He wrote: "I met somebody the other day who told me that online networking was so important, and he didn't have the time, he was paying somebody to be him online. To blog, network, post etc . £1,000 a month too.
"Apparently it's a new occupation which he reckons already numbers hundreds of people, paid to be other people!"
I rang the sender of the message - a real-world friend as well as a Facebook contact - and he gave me more details.
"This guy is a busy entrepreneur and he says that wherever he goes, people marvel at the energy he still manages to put into blogging and networking - and he then tells them it is all being done by a guy he pays to do it."
It's well known that Chinese workers spend long hours earning "gold" on the online game World of Warcraft, so that busy Western gamers can buy a new sword without putting in an excessive amount of time in front of their computers.
But are there really crowds of busy executives hiring others to do the online dirty work for them?
One of the things I like about Facebook is that its users appear to be there under their own identities - rather than the "lonelygirl15" of YouTube, or "crazyguy1603" on MySpace.
I started worrying about some of my Facebook "friends". Were they who they said they were?
What about Brent Hoberman, the founder of lastminute.com, and one of the elite members of London's "digerati"?
Brent Hoberman, the founder of lastminute.com, has a genuine page
Surely a busy man like him, in the middle of starting up a new online venture, does not have time to update his status on Facebook, ask his friends about their favourite books and films and take part in discussions about TV property programmes?
When I contacted him he assured me (via a blackberry message, mind you) that this was the real Hoberman.
"I think if I could get someone else to manage my e-mail then I could outsource social networking," he said.
"But I can't, and think one has slightly lost the plot if that happens."
Good, so he's the real him.
But what about my dear friend Sir Patrick Moore? I joined up with him a couple of weeks ago and was not entirely convinced he was the great astronomer.
His profile said he was here for "random play" and "whatever I can get" and his home town was Pinner.
I happened to know that Sir Patrick lives in Selsey, in Sussex, so I wrote seeking reassurance.
Patrick Moore has a Facebook page - or does he?
"It is definitely me," he replied some days later, "extraordinary as it may seem! I was told about Facebook by some young camera crew I was working with, you see, and I was intrigued how people are able to communicate these days.
"You 're quite right I do live in Selsey, Pinner is the town in which I was born."
Hmm, still not entirely convinced.
And then there is Stephen Fry.
As an admirer of the great comic writer and actor (and gadget obsessive) I was delighted to spot him on another friend's network.
And even more pleased when my friendship request was accepted.
But his friends list appeared to be growing at an alarming rate, he was busy asking questions, playing rock, paper, scissors, and describing his favourite artists using the "ilike" application.
Surely this was the work of a gifted assistant?
Then came his latest status update: "Stephen is...concerned about the number of friendship requests he's getting. Don't want to turn anyone down, but 20+ every hour and rising is getting to be a worry."
Confirmation, then, that this was the real Stephen Fry, facing one of the dilemmas of modern manners - how to politely decline an offer of online friendship.
The actor has now set up a friendship group as a point of contact for all those strangers who want to be his friends.
But, like millions of others, he seems to have caught the Facebook bug.