Microsoft just made millions off a 14-year-old product it shut down a year ago

To Microsoft, Windows XP is like a gift that keeps on giving.

Even though Microsoft stopped selling Windows XP in 2010 and completely shut down support updates a little over a year ago, it's continuing to make money off of it. It's because there's still a huge customer base using Windows XP and they're willing to dole out millions of dollars for custom security support.

The latest customer to sign a Windows XP support deal is the US Navy.

On Tuesday, the Navy's Space and Naval Warfare Systems Command (SPAWAR) closed a $9.1 million contract with Microsoft that guarantees continued custom support for security updates on the 100,000 workstations still using Windowx XP, Office 2003, Exchange 2003, and Windows Server 2003.

The full contract could extend to 2017, and be worth up to $30.8 million, IDG News added.

"The Navy relies on a number of legacy applications and programs that are reliant on legacy Windows products. Until those applications and programs are modernized or phased out, this continuity of services is required to maintain operational effectiveness," Steven Davis, a spokesman for SPAWAR, told IDG.

The US Navy is certainly not the only public office to sign a big custom contract with Microsoft. The UK government signed a $9.2 million contract last year to support all public sector customers, while the Dutch government also signed a "multi-million euro" deal for a similar service.

A lot of these organizations rely on old software that only runs on Windows XP, which makes it hard to migrate everything over to a new OS. But with Microsoft effectively ending support for Windows XP last year, they need custom security updates to protect them from external threats.

In fact, according to NetMarketshare, a research firm that tracks OS usage, Windows XP still accounts for roughly 14% of the total desktop operating system market. That's more than the market share of Windows 8.1, Microsoft's latest operating system.