Windows is not fully updated
hackers and virus writers are constantly looking for bad written code in Windows in order to penetrate windows with a virus or a hack. When they find a way to penetrate, they will create a virus to attack that portion of Windows.
When Microsoft discovers the bad written code, they will write an update to close the issue and put it on their update site. It is very important that you run Windows update at least if not more than once a week to get the latest updates.
If you just installed Windows, it is very important to run the updates as soon as possible. When you run the updates, repeat the updates till the update site states there is no more updates available.