NO_PUBKEY

Hey Guys,

FOr the last several security updates I have just been doing
apt-get update
apt-get upgrade
so that I might also pick up other operating system items that may be available. This has worked just fine and seems to continue to work fine however, lately when I do the update I get the following message:

W: GPG error: http://software.virtualmin.com virtualmin-dapper Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E8DD3FA0A0BDBCF9

Being still quite green in some areas of linux, I'm not sure how to proceed with a remedy for this or if I should even worry about it. I just know it didn't do this until just a couple of months ago.

Thanks in advance!

Tom