You may not be able to see or hear it, but new research has found that one in five Mac computers carry Windows or Mac Malware.

Sophos experts tested 100,000 Macs and found an alarmingly high number of computers that carry one of the two malware. 

Most of the Macs were found carrying Windows malware, which doesn't explicitly show symptoms on Macs ( apart from ones with Windows installed.) But they found that Macs were capable of spreading the windows malware onto other computers. 

Mac OS X malware was also found during the research, but was not as common with one in 36 Macs carrying the virus. 

Some Mac users may be relieved that they are seven times more likely to have Windows viruses, spyware and Trojans on their Macs than Mac OS X-specific malware, but Mac malware is surprisingly commonly encountered, said Graham Cluley, senior technology consultant at Sophos. Mac users need a wake-up call about the growing malware problem.

Sophos researchers warn that malware can spread easily through emails, attachments, USB devices and even Website downloads. During their research, Sophos experts found computers that had been carrying malware since 2007, which could have easily been prevented had the user carried out a test. 

The simple fact is that you can scan your Mac for infection from your armchair. The test is painless and free; you just download an anti-virus product and allow it to check your computer and protect it against infections in the future, says Cluley.

How to Check for Malware

Users who want to check their Macs at home can download the antivirus software can be downloaded at: .Cult of Mac also offers Malware checking and removal, which can be found here. 

Flashback Trojan Horse 

In early April, hundreds of thousands of Mac users were subjected to a Flashback Trojan Horse virus, which continued to spread despite various attempts to eliminate the virus with software updates and removal tools. 

Most cases of the malware have been removed, but for those who want to make sure their Mac isn't infected a free Flashback checker has been released and can be found here.