Microsoft may have ended support for Windows XP in April, but 18 percent of small and medium-sized businesses (SMBs) still use the operating system and face security risks, according to research from antivirus software provider Bitdefender.

After conducting research from March to May 2014 on 5,000 companies in the U.K., the U.S., Spain, Germany and other countries, Bitdefender found 53 percent of the companies had upgraded to Windows 7 Professional.

But with malware on the rise — one web marketing business reviewed had to fend off more than 800 million malware attacks — and more employees working remotely — 37 percent — SMBs using XP are at risk.

Microsoft no longer offers new security updates, non-security hotfixes, free or paid assisted support options or online technical content updates for XP, though the company did recently release an unscheduled zero-day patch for Internet Explorer that benefited the operating system.