Been sent this:
Apple has released macOS 11.6 Big Sur, iOS 14.8, iPadOS 14.8, watchOS 7.6.2, and Security Update 2021-005 Catalina to fix "a PDF-related security issue" and a Web browsing vulnerability: “Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.”
These are the software holes exploited by Pegasus spyware to target Bahraini activists, among others. It completely takes over your device and can be used to extract any and all data. Whereas Pegasus spyware is mostly used by government agencies against specific individuals, the exploit mechanism is now known and will soon be on sale on the dark web, if it's not already.
If you're using Big Sur or Catalina, stop what you're doing and install these, please. This one is urgent. On iPhones and iPads the update is in Settings/General/Software Update. On the Mac, go to System Preferences/Software Update, where the update will appear after a few moments. If you're on Catalina and offered Big Sur, click on the blue text "More Updates".
If you're still using an older operating system it's time to consider getting up to date. If you don't you'll probably be had by a malicious phishing iMessage or email sooner rather than later.