DVDs mirrored on http://localhost is untrusted

[Martin <adsrtg-mlist@yahoo.com.au>]

Hi,

I have copyed all DVDs to external USB HD and made it available to
aptitude as described in http://www.debian.org/CD/faq/index.en.html. It
works fine but everytime I install a package I get a warning something
like:

┌────────────────────────────────────────────────────────────────────────────┐
│WARNING: untrusted versions of the following packages will be installed!    │
│                                                                            │
│Untrusted packages could compromise your system's security.  You should only│
│proceed with the installation if you are certain that this is what you want │
│to do.                                                                      │
│                                                                            │
│  * wamerican [version 6-3]                                                 │
│  * bsdgames [version 2.17-19]                                              │
│         [ Really Continue ]                  [ Abort Installation ]        │
└────────────────────────────────────────────────────────────────────────────┘

How can I get rid of this warning?
Martin