One in five Macs is harboring malware, says security firm Sophos - and not just the native kind but the Windows variety too.
The company analyzed around 100,000 Mac computers running its free anti-virus software, and found that a fifth were found to be carrying one or more instances of Windows malware.
Although Windows malware on Macs won't cause symptoms unless users are also running Windows, it can still be spread to other computers - indeed, senior technology consultant at Sophos helpfully compares it to the often symptomless sexually transmitted disease chlamydia.
But while Mac users may not be too bothered about Windows malware, Sophos also found that one in every 36 Macs was carrying Mac OS X malware.
"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 being surprisingly commonly encountered," says Cluley.
"Mac users need a loud wake-up call about the growing malware problem."
The most common Mac-based threat are 'anti-virus'scareware attacks and the recent Flashback botnet - belived to have infected more than 600,000 Macs worldwide.
"Mac malware can spread via USB stick, email attachments, website download, or even a silent drive-by installation where the user doesn't realise their Mac's security has been subverted," says Cluley.
"Cybercriminals view Macs as a soft target, because their owners don’t typically run anti-virus software and are thought to have a higher level of disposable income than the typical Windows user."