The company is also working with internet service providers to disable the "command and control network" that hackers are using to exploit the malware. According to Info World, that means asking hosting firms to pull hacker-operated servers off the internet so that infected computers cannot receive further orders.
The announcement is Apple's first public statement on the threat since anti-virus software developer Dr. Web reported that 550,000 Macintosh computers had been infected by last week. Apple released a software update that helps the unauthorized installation of the malware, but this new tool should help users whose computers are already infected.
The company has not said when the tool will be made available to the public, CNET reported.
Dr. Web now estimates that 650,000 Macs have been affected worldwide.
The Flashback virus was first discovered by anti-virus experts in September 2011. It was initially designed to resemble an Adobe Flash Player installer, but would seek out stored user names and passwords. Later versions of the botnet exploited weaknesses in Java programs and allowed the virus to be installed from certain websites without the user's permission.
The outbreak, said to be one of the biggest security issues yet faced by Macs, has shattered OSX's reputation as a "virus-free environment," said PC Mag, which advises all Mac users to install anti-virus software.
"Mac users thought that they can practically do whatever they want on the internet, with no risks involved," Catalin Cosoi, chief security researcher for anti-virus firm Bitdefender, told the website. "Unfortunately, the bad news is that even though this was probably the largest infection so far, it’s probably not enough to convince Mac users that the threat is real and it's here to stay."