A year and a half after Microsoft stopped supporting it, Windows XP is still heavily used by both small and mid-sized companies across Eastern Europe, as well as by the public sector, an analysis conducted by security company Bitdefender shows.

Ukraine leads the nostalgic group. Windows XP runs on 41.2 percent of business and public computers that use Bitdefender's antivirus software. Hungary follows with 37.5 percent, while Romania ranks third with 34 percent.

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Next in line are Poland (24.05 percent) and the Republic of Moldova (18.7 percent). Other countries such as Slovakia (10.61 percent), Bulgaria (six percent), and the Czech Republic (4.7 percent) are finding it easier to upgrade to a more recent version of the OS.

"Some might choose to continue using Windows XP because of legacy issues with proprietary applications and systems," Liviu Arsene, senior e-threat analyst at Bitdefender, told ZDNet. "Internal software that hasn't been updated most likely isn't compatible with Windows 7 or 8.1."

He adds that Windows XP vulnerabilities that have been discovered but haven't been patched are the easiest way of attacking a computer. "Migrating to a more recent version won't just add features, it will also increase security," Arsene said.

He estimates that Windows XP's market share will continue to drop both globally and in Eastern Europe, as the "security implications will no longer be negligible".

"It all boils down to how much your personal and sensitive files are worth to you, and whether or not anyone would have anything to gain by accessing and selling them."

Windows XP in Romania

Several small Romanian companies in accounting, insurance, and construction contacted by ZDNet admitted they still use the retired OS.

Application compatibility remains a reason for some to continue using the old OS, while other factors mentioned were emotional attachment to the software that delivered as expected, hardware and software upgrade costs, and lower productivity during the transition cycle.

Bitdefender published a similar study last year in July. Back then, Windows XP's market share was 23 percent higher than today. In the business and public sector as a whole, it accounted for 57 percent of machines, but in the public sector alone, the figure was much larger: the OS was present on 70 percent of systems.

NGOs and population

Non-governmental organizations in Romania seem to be better at upgrading: the large majority of them use Windows 7 and 8.1, Elena Coman, programs director for Techsoup, a not-for-profit organisation that provides tech services to the voluntary sector, told ZDNet.

"Microsoft is TechSoup's first partner in Romania and has been donating software since 2009," Coman said. "The [total] market value of their donations exceeds $3m. It's by far the largest contribution made by a technology company to the local NGO sector."

The latest StatCounter data, which takes business clients and consumers as a whole, estimates that Windows XP was installed on 14.5 percent of Romanian PCs at the end of this August, compared to 24.9 percent a year ago.

Microsoft's data

A Microsoft spokesperson in Romania told ZDNet that their market share estimations for Windows XP are "significantly lower" than Bitdefender's numbers. However, the company declined to share their data or to comment further.

Bitdefender is a major security vendor in Romania, with a large consumer and enterprise install base.

The company counts both legitimate and pirate OS copies, and software piracy across Eastern Europe is estimated at 62 percent, according to the latest BSA global software survey.

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