Specter is one of two dangerous CPU vulnerabilities that have just been revealed last week on devices running Intel, AMD and ARM chips. Earlier Apple released an update for Meltdown in the first update over a month ago.
Although updating OS is always necessary, there are times when you wait for a while to do it. But these security updates are very important because Meltdown and Specter are so dangerous that most users should update immediately. It is not clear whether Apple's A-Series processor needs a separate patch.
Microsoft and Google have already released updates. Read detailed information about Apple's announcement here: https://support.apple.com/en-us/HT201222.
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