The “vast majority” of Mac users are safe from Shellshock, the latest computer security vulnerability which could allow hackers to take over an operating system.

An Apple spokesperson told iMore that only advanced users are likely to have enabled the types of services that could be exploited by the bug.

“With OS X, systems are safe by default and not exposed to remote exploits of bash unless users configure advanced UNIX services,” said the spokesperson. “We are working to quickly provide a software update for our advanced UNIX users.”

The Shellshock vulnerability affects Linux- and Unix-based operating systems, including OS X and millions of computers and devices throughout the world. According to CNET, the exploit is based on execution of malicious code within what is known as a “bash shell,” or the command-line shell used in these operating systems.  The bug enables an attacker to bypass regular security controls to insert unauthorized commands that could allow the attacker to steal data or gain control over the web server computer or other device.

Unfortunately, as with the Heartbleed bug identified last April, there is very little that ordinary computer users can do to protect themselves from the flaw. Steps to patch the vulnerability must be taken by those who actually manage web systems. But if Heartbleed is any guide, many of those individuals will be slow to act. CNET reports that two months after researchers identified Heartbleed, 300,000 servers remained exposed.