In the computing world, open-source software is often taken to mean free - so why would a charity choose to fork out good money for proprietary software?
Microsoft offers cheap software to charities
The theory behind open-source software is that it avoids many of the pitfalls - including cost - of closed alternatives.
But Steven Buckley, who runs Christian Aid's common knowledge programme, prefers to buy software from the likes of Microsoft. Is this not odd for a charity?
"Open-source doesn't mean free," he told BBC World Service's Digital Planet programme.
"Quite often, if you install open-source software within an organisation, you have a support contract that goes with it - it's an essential part of operating that software.
"Over time, that can actually cost more than having Windows on an enterprise machine."
Mark Shuttleworth, an evangelist for open-source software based on the Linux operating system, recently told Digital Planet that the software was "on its way to becoming one of those standard, de facto platforms".
But Mr Buckley said that Linux is not widely-used enough for the charity's staff to be proficient at it, meaning that there is a cost to the organisation in terms of skills.
"Microsoft skills are easily available throughout the world in terms of an organisation, and it is more effective for us to have Microsoft software which we can employ people easily for," he said.
Linux is among the most used of the open-source programs
"Open-source software can be expensive to be configured, and the knowledge of the software is with only a few people."
He also explained that what is seen as one of the advantages of open-source - that the core code can be examined by anyone - could actually work against the charity.
"We are a funding organisation that ships £90m around the world - the last thing you want to do is open up your systems to anybody to have a look at to deal with bugs," he said.
"So you do need a support model in place. But one of the things that we find is that Microsoft is viewed as the big, bad organisation - but they've actually got some good corporate social responsibility.
"If you're a charity or an educational institution, you pay pence in the pound for the licence, compared to what a major bank might pay."
He stressed that it was important for charities to maximise the benefit of the donations they receive, and as a result, using Microsoft appeared a better option.
Open source fan Mark Shuttleworth was one of the first space tourists
"When you think of charities, we think they are liberal organisations with woolley-jumpered amateurs - but really, we've got a duty of care to our supporters," he said.
"We spend one pence in the pound on administration, and that means we've got to be as effective and efficient as we can, and software is one way to do that."
However, technology analyst Bill Thompson pointed out that it was a misconception that open-source means free that makes a charity opting for proprietary software seem surprising.
He said that as a charity, Christian Aid got a discounted price for the software from Microsoft. He pointed out that there was a great deal of technical support available for Linux too.
"The idea that Linux can just be installed and used is not necessarily the case - there are usability issues with the desktop, and some with connecting various bits of hardware to the Linux system," he added.
"But it isn't as simple as saying, 'Linux is complicated; Windows isn't." These are all complex systems, and the key thing is generally to find something that works for you."
You can hear this story in full on this week's edition of Digital Planet with Gareth Mitchell.