There have been some bogus emails recently with a subject of “Microsoft Security Update“. It contains a whole lot of text encouraging you to click on a link to install a security update. If you look at the email carefully you might notice that it contains a link to a website not owned by Microsoft, and instead it will attempt to download and install a virus.
How are you supposed to know it’s false? For a start Microsoft probably doesn’t know who you are or what your email address is. If you’re a home user it’s very uncommon (and unnecessary) to register your address with them. And even if you did, email is not the method Microsoft uses to advise you on updates or to distribute the updates.
For business users, you have an IT department that takes care of all updates. You shouldn’t be trying to install security updates so treat any such email as bogus.
Bottom line: delete these emails. Any good spam or virus filter should catch most of them, and it’s best to be cautious.