Almost one in five (18%) of small and midsized businesses worldwide are putting themselves at risk of a major security breach by remaining on Windows XP after its April 8 end-of-support date.

The finding comes from a study by antivirus vendor Bitdefender, which surveyed more than 5,000 companies in areas including retail, healthcare and education between March and May 2014.

More than half (53%) of companies had upgraded from Windows XP to Windows 7 Professional, while only "a small percentage" said they are running a different version of Windows - such as Windows 7 Home or Windows 8.1.

Those that remain on the 12-year-old Windows XP, which some call the "operating system that never dies" due to its still-widespread use, are engaging in a security 'Russian roulette' as Microsoft no longer issues security updates or technical support to users, making them more susceptible to malware attacks that can steal confidential data.

Risky business

According to Bitdefender, one web marketing business had to deal with almost 800 million malware attacks during the three-month observation period.

Catalin Sosoi, Chief Security Strategist at Bitfdefender, said: "A few weeks after the end of support announcement, a new Internet Explorer zero-day vulnerability turned into a permanent threat for XP users.

"That was until Microsoft issued a patch that was made available for Windows XP users as well. However, this was an exception that shouldn't make enterprises believe it will happen again, so the swift migration from XP is a must for all users."