Secunia upgraded the level of the Safari, Internet Explorer advisory Tuesday "because the issues are very easy to exploit and a large number of working exploits are available," according to the updated advisory.
Typically, people write exploits and other forms of malicious code for the Windows operating system because so many people use that OS and because of the notoriety the person gets. For those same reasons, Macs are usually spared.
"It seems to be that people just don't write exploits for the Mac because they're not as popular and they (the exploit writers) don't get much bang for the buck," said Bruce Schneier, CTO of Counterpane Internet Security. "Historically these aren't that big of a deal, but that could change."
In a statement this evening, Apple said they were investigating the potential security issue.
"We take security very seriously at Apple and we are actively investigating this potential security issue," Apple's statement read. "While no operating system can be completely secure from all threats, Apple has an excellent track record of identifying and rapidly correcting potential vulnerabilities."
Representatives from Secunia were not immediately available to comment further on the advisory.