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Welcome to the forums, BDP!
As long as automatic updates is checked, the Avast! program will check for updates to the program and virus data base (VBD) definitions shortly after you connect your computer to the internet. It will then check for updates again every four hours if you are connected for that long.
You should get an update of the VDB at least once a week. If, by chance that does not happen, please come back and make a new post so that someone can help you.
And welcome to Avast ... be sure to come back often, learn more, and maybe help others!
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