Details of the flaw haven't been made public, so it's unlikely that anyone is going to write a worm any time soon. But the bug is serious, according to Gordon Maddern, the Australian security researcher who reported the issue to Skype.

"The long and the short of it is that an attacker needs only to send a victim a message and they can gain remote control of the victims Mac," . "It is extremely wormable and dangerous."

According to Skype, any attack that exploited it would involve sending a maliciously crafted message to someone on the attacker's Skype Contact List. The flaw does not affect Windows or Linux users, Skype Chief Information Security Officer Adrian Asher

Skype will push out an update to its Skype for Mac software early next week, which means that all Mac OS users should be offered the fix within days.

But security-conscious people can already download a "hotfix" that Skype released on April 14. However, to date, Skype hasn't pushed this patch out to its users. Because "there were no reports of this vulnerability being exploited in the wild, we did not prompt our users to install this update," Asher said.