Digital do-gooders: Why do we help strangers online?
All around the world, more and more people are donating their time to take part in online volunteering projects. What motivates them to help strangers without expectation of money or even thanks?
Radha Taralekar helped teach Imelda how to protect herself from HIV, though the two have never met, and neither knows the other's name.
From her home in Mumbai, the young doctor took several weeks to co-write a guide especially for Imelda - who lost her children to HIV/Aids - and her friends at the Kitega Community Centre in Uganda.
She received no payment for the job, which was advertised on a United Nations website aiming to connect office-based volunteers with those in need of help.
To the traditional volunteer it may sound a world away from serving food to the homeless or sorting clothes in a local charity shop. There are no warm smiles, no nods of appreciation and phone calls are sporadic, if they come at all. Instead, thanks may arrive by email or instant message.
Taralekar is one of a number of talented individuals who regularly donate their time online. But what is driving them to help total strangers, while asking for nothing in return?
For Taralekar, the project gave her the chance to work with people overseas without leaving her own country. "I'm just not very money driven. I want to serve people, I want to come up with ideas," she says.
Kate Anderson, another online volunteer, used to help out at a local soup kitchen in Georgetown, Washington DC where, she says, "lots of people were just standing around. It wasn't helpful".
Instead she chose to file grant applications from her home in the US for a charity in Pakistan which, she says, was a far better use of her professional experience.
For others the inspiration to volunteer online was far more personal.
After losing his wife and sister to cancer, Tony Selman spent many hours helping Cancer Research to analyse data on the disease. He uses Cell Slider, a website that asks members of the public to review microscopic photographs of tumour samples and place them in different categories.
"I have the knowledge of how dreadful these diseases are. I sat with my wife as she died. It's not an altruistic issue. It's the knowledge that you can contribute something and get satisfaction from it.
"To be honest, it's one of the things that keeps me sane," he says.
In 2011 Sam Luk, a Manchester-based designer, joined other online enthusiasts to try to help the FBI solve a murder case.
Twelve years earlier the body of Ricky McCormick had been found murdered in a field in St Louis, Missouri - the only clues being two encrypted letters found in his pockets. Unable to decipher the codes, the FBI posted them online, calling for volunteers to help them make sense of the encoded messages.
"I'm interested in patterns and I love Sherlock Holmes," says Luk.
But there was also a social element to his work. He wrote a blog about the project because he wanted to connect with like-minded people. "It was an outlet to get across things that I can't chat to my mates about."
Luk spent hours trying to decrypt the notes, but the message eluded him, and the case remains unsolved to this day.
For writer and web theorist Clay Shirky, this lack of interest in financial gain is understandable.
He argues that we have become so accustomed to the idea of market forces governing our society that "we forget that most people do most things without getting paid for them".
"Anything that gives me a sense of membership or generosity gives me positive feedback of the sort that I cannot get merely from earning money," he says.
Shirky thinks educated people around the world have about a trillion hours of free time each year that could be contributed to collaborative projects, a phenomenon he calls "cognitive surplus".
Websites such as Help from Home encourage people to volunteer as little as a few minutes of their time. But some online volunteers are willing to undertake projects on a scale that far outweighs this "micro-volunteering".
Wikipedia, for example, the world's biggest encyclopaedia, is written entirely by contributors willing to donate their expertise without monetary reward.
And vast, complex pieces of open-source computer software have been pieced together by armies of committed developers, often working for nothing.
Brian Behlendorf, a web pioneer who helped create Apache, a piece of software that now underpins much of the world wide web, says a sense of rebellion against Microsoft - who had become a dominant force in the desktop PC market - was one of his main motivations.
"There was an idealism there," he says. "We didn't want the internet to go the same way as the desktop. We knew that open software was best for everyone except one or two people at the top."
There are also purists who see writing code as an art form in itself - it can be "ugly" or "beautiful" - and strive for ever more elegant forms of code, according to author Steve Weber, who has written on the success of the model.
"Is it altruistic? That's a bigger question than I'm willing to take on," he says. "But I think it would be wrong to assume that there isn't a meaningful set of people who just think 'Hey, I'm going to do this and give it away because it's good for the world.'"
At the Kitega Community Centre in Uganda, volunteer co-ordinator David Clemy agrees that those who help his charity from their respective homes around the world are spurred on by a sense of idealism.
"They want to change the world," he says. And he is no doubt about the value that they bring to Kitega.
"Without the online volunteers, the project would be 20 years behind where it is today."
There are more volunteering stories in the BBC News series Making Time