A McAfee study of PCs around the world found that 17% had no antivirus protection.

The study counted as unprotected machines those that had no antivirus protection installed, or whose antivirus subscription had expired. In the US which outpaced the average, 12% of PCs did not contain any antivirus program, and 7% had software that was expired.

McAfee analysed data from voluntary scans of 27 million machines in 24 countries. According to the company, the study was the first to examine machines directly rather than polling their users. User polls have typically found that 6% of PCs are not protected by antivirus software, Gary Davis, McAfee's director of global consumer product marketing, said.

"People know it's correct to run antivirus," Davis explained. In some cases, they may believe their software subscription is still active when in fact it has expired.

PCs in Finland, Italy, New Zealand, Germany and Denmark were most likely to be protected, the study found. Those in Singapore, Spain, Mexico, Japan, and the United States were least likely to have active antivirus protection.

"We thought for sure the US and Japan would be at top of protected countries, but they were actually at the bottom," said Davis.

Spain had the highest percentage of PCs without any installed security protection at 16%. Singapore had the least secure computers as well as the highest percentage of users with disabled security protection with 12%.

User education may help reduce the number of unprotected machines, Davis said. Updates to Windows 8, which requires active antivirus protection, may also help, he said.