Warning message in update manager: software that "can't be authenticated!"

[stevieP]

For some reason I am getting a Warning message in update manager that says:

"You are about to install software that *can't be authenticated!* Doing this could allow a malicious individual to damage or take control of your system.

I've gotten this a few times in the past when doing updates and ignored it, but I don't want to keep ignoring messages like this when doing updates.

The updates I was going to install were:
python-apt
language-pack-en
language-pack-gnome-en
tzdata
esound-common
libesd-alsa0

(I never installed them)

I've attached a screenshot below.

Here is my computer info:
% uname -a
Linux bowie 2.6.22-15-generic #1 SMP Fri Jul 11 19:25:33 UTC 2008 i686 GNU/Linux

Here is output from
% cat /etc/apt/sources.list



# deb cdrom:[Ubuntu 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

# Line commented out by installer because it failed to verify:
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy main restricted
# Line commented out by installer because it failed to verify:
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy main restricted

## Major bug fix updates produced after the final release of the
## distribution.
# Line commented out by installer because it failed to verify:
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy-updates main restricted
# Line commented out by installer because it failed to verify:
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
# Line commented out by installer because it failed to verify:
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy universe
# Line commented out by installer because it failed to verify:
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy universe
# Line commented out by installer because it failed to verify:
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy-updates universe
# Line commented out by installer because it failed to verify:
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
# Line commented out by installer because it failed to verify:
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy multiverse
# Line commented out by installer because it failed to verify:
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy multiverse
# Line commented out by installer because it failed to verify:
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy-updates multiverse
# Line commented out by installer because it failed to verify:
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://ca.archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse
# deb-src http://ca.archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
# deb http://archive.canonical.com/ubuntu gutsy partner
# deb-src http://archive.canonical.com/ubuntu gutsy partner

# Line commented out by installer because it failed to verify:
# deb http://security.ubuntu.com/ubuntu gutsy-security main restricted
# Line commented out by installer because it failed to verify:
# deb-src http://security.ubuntu.com/ubuntu gutsy-security main restricted
# Line commented out by installer because it failed to verify:
# deb http://security.ubuntu.com/ubuntu gutsy-security universe
# Line commented out by installer because it failed to verify:
# deb-src http://security.ubuntu.com/ubuntu gutsy-security universe
# Line commented out by installer because it failed to verify:
# deb http://security.ubuntu.com/ubuntu gutsy-security multiverse
# Line commented out by installer because it failed to verify:
deb http://archive.ubuntu.com/ubuntu/ gutsy main universe
deb http://security.ubuntu.com/ubuntu/ gutsy-security restricted main universe
deb http://archive.ubuntu.com/ubuntu/ gutsy-updates restricted main universe
# deb-src http://security.ubuntu.com/ubuntu gutsy-security multiverse


Thanks,
stevieP

[iaculallad]

It's OK to continue installing the updates. Probably you had enabled your backports and included third party softwares in your repository.

[stevieP]

OK. A couple questions then-

What does it mean to enable my backports?

What are the criteria a third party has to satisfy to be able to deposit software in the repository? Can anyone do it? (If so, it doesn't inspire a lot of confidence).

Thanks,
stevieP