It's safe to say that virtually every enterprise is already using open source somewhere. It has always been used in infrastructure solutions - the DNS, and basic networking facilities. But increasingly it's now also used throughout the so-called "enterprise stack" - in application servers, and in integration and storage solutions. And let's not forget that the core of the most widely used smartphone operating system, Android, is open source. [See also: Open source in the enterprise - 16 CIOs embracing free and open source software]

Why has open source become so prevalent? One might easily think that open source software saves money. After all, users of open source spend little or no money upfront. Or one might think that open source software reduces vendor lock-in. If it's open, how can you get roped into working with one supplier?

But it turns out that both these notions are misleading. According to Gartner analyst Arun Chandrasekaren: "Open source software typically increases operating expenditure (opex), which must be carefully balanced with the reduction in capital expenditure (capex). For example, many Gartner clients have cited that OpenStack requires hundreds of hours of integration and maintenance in addition to what commercial alternatives require."

As for the notion that one can avoid vendor lock-in through open source, Chandrasekaren warns: "Vendors often market proprietary approaches as 'open,' which can lead to vendor lock-in and high switching costs."

So what are some of the real drivers behind the proliferation of open source in the enterprise? It turns out that even though open source software comes with hidden costs and doesn't always solve the problem of vendor lock-in, using open source puts you on a faster track to the digital future. Lebara CTO Finbarr Joy says: "Open source communities are typically pushing the envelope in digital capabilities. This is evidenced by the significant advances in Big Data, machine learning, and DevOps - all driven by open source communities."

Having free access to some of the best-written code in the world comes with other advantages. According to Joy: "When you use open source you can hire better engineers, because the best engineers want to work with open source."

What's more, open source software is typically very stable. CTO at Nominet UK, Simon McCalla says: "One of the advantages of open source is that it's heavily deployed and heavily tested. In our case, the fact that it gets used for billions of queries every day means that most of the bugs have been ironed out a long time ago."

Open source has come a long way since the early days. Most of the world's best engineers now contribute significant time and effort to developing open source software. Many of the largest technology vendors sponsor open source initiatives - Hewlett Packard Enterprise and IBM are two names that come to mind. Perhaps the most surprising change is that even Microsoft has become a major contributor of open source software.

Vendors are jumping on the open source bandwagon, because thanks to cloud computing, there are new ways of making money on software. Rather than sell software licenses, companies like Microsoft can give away source code, while at the same time, selling a subscription to use the software in the form of a cloud service.

What's in it for the customer? Futurist at Jisc, Martin Hamilton, explains: "In the educational sector, the popular Canvas virtual learning environment is an open source product. Even though you can download it, install it, and change it yourself for free, most people prefer to pay to have it hosted for them. For the customer, the source code is always there as an insurance policy. It's a nice counterbalance to the uncertainty you may experience when you acquire a product from a small or unfamiliar firm."

As for the development community, Finbarr Joy reckons that good engineers have four good reasons to jump on the open source bandwagon. Contributing to open source is an outlet for creativity, it provides developers the sense of being part of a bigger purpose, engineers gain in prestige by contributing to open source, and finally, developers might get paid money for supporting open source products or providing consulting services as product experts.

Open source can't be used everywhere though. IS director at United Utilities, William Hewish says he recently used open source software for rapid prototyping: "We needed to find out how far we could stretch our middleware, so we used open source to help us prove some concepts very quickly. Meanwhile, we worked what we learned into our conventional software."

Hewish says he wouldn't use open source software for employee-facing applications. "We avoid open source for anything around the desktop for instance, because with more established products, training is minimal, and we don't have the burden of managing security threats and patches. The vendor covers that."

Finally, Hewish says he avoids open source for any application that is an integral part of the business - for example, a large ERP system. "If there's a problem," Hewish says, "I need a vendor who feels obliged to be with us 24 by 7 to work through the problem and protect their name."

IT directors should also pay careful attention to open source license agreements. According to Simon McCalla: "You have to review an open source license in the same way you review any other license. How proprietary is this? What traps are there?"

"A lot of open source software is built on other open source libraries," says McCalla. "These libraries may have bugs in them - even worse, they might present security threats. Pay special attention to what the software license says about the use of libraries."

[Now read: Overcoming barriers to open source - Tackling the business case for open source]