Apple is recommending that Mac users update their systems after revealing that hackers had exploited two vulnerabilities in its software. The company issued two bug fixes on Tuesday addressing issues in WebKit and JavaScriptCore,

In a security advisory on its website, Apple said it was aware of two vulnerabilities that “may have been actively exploited on Intel-based Mac systems.” The bugs are considered “zero day” vulnerabilities because they were unknown to Apple at the time they were exploited.

The security gaps have already been actively exploited in hacking attacks, Apple says. Apple has not released details about the security issues, but they say the update “provides important security fixes and is recommended for all users.