Windows Defender is designed to update via AutoUpdate.
There are a few cases of home users who find that the autoupdate doesn't
work properly until they've done a Windows Update run--in some cases they
seem to be missing some previous update, in other cases, somehow getting the
first set of updates into place seems to cause the automatic mechanism to
work right the next time around.
The reason I/we harp on using Windows Update is that we can't tell from the
majority of initial posts here whether the user is on a managed corporate
network which restricts how AutoUpdate functions--that is behind a large
proportion of the "update failures" cited here. If the network is fully
locked down, the user won't have access to Windows Update either, and thus
this fact will come out. If autoupdate is restricted, but Windows Update is
available, then updating will succeed over Windows Update--and we can talk
about why it is that AutoUpdate doesn't work.
If you are a home or small network users, and Windows Update and AutoUpdate
work and connect directly to Microsoft--definitions should come in
automatically.
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