Anti-virus vendor Doctor Web claims that at least 550,000 Apple devices from across the globe have been infected by the Backdoor.Flashback botnet.
The Russian vendor said that nearly 13 per cent of the affected devices are located in the UK, although the vast majority (56.6 per cent) are US-based.
"This once again refutes claims by some experts that there are no cyber threats to Mac OS X," said the firm in a blog post.
However, in a tweet sent by Doctor Web malware analyst, Sorokin Ivan, it was claimed that the actual number of affected devices could be slightly higher than first thought.
"This once again refutes claims by some experts that there are no cyber-threats to Mac OS X."
"At this moment botnet Flashback [has infected] over 600k [devices], include[ing] 274 bots from Cupertino," he wrote.
The blog post also explained that the infection starts when Mac users are redirected to compromised websites containing corrupt JavaScript code.
Once installed, this file is used to download malicious content from a remote server, which is then activated.
It is also claimed that, at the end of March, links to more than 4 million sites, containing this code, could be found among the search results on Google.
