According to The Register, the latest version of Skype for the Mac has a serious security flaw.
The bug would allow an attacker root access to the Mac by attaching a specific file to an IM chat.
Gordon Maddern of Australian security consultancy Pure Hacking discovered the issue, and alerted Skype about the security hole. Maddern was told:
Thank you for showing an interest in Skype security, we are aware of this issue and will be addressing it in the next hotfix.
The bug isn’t present in Windows or Linux builds of the program, but thankfully Maddern has said he will not disclose the security bug to the public.