Debian - "WARNING: untrusted versions of the following packages will be installed!"

Solution 1:

Try this please:

Open a terminal and run the following commands:

sudo apt-get clean
sudo rm -rf /var/lib/apt/lists/*
sudo apt-get clean
sudo apt-get update

Solution 2:

After reading APZ's answer, but wanting to use aptitude I executed with success the following commands:

# clean the obsolete cache
sudo aptitude clean
# update the package information
sudo aptitude update
# install or upgrade the packages
sudo aptitude install <list of packages to upgrade/install>

The error is probably related to obsolete apt cache contents, but the error message I got was a bit different:

WARNING: untrusted versions of the following packages will be installed!

Solution 3:

You seem to be hit by Debian bug #657561. You can try to move problematic /var/lib/apt/lists/*InRelease files and rerun apt-get update.