Sometimes when performing your daily
apt-get update, you'll experience messages like
E: The package lists or status file could not be parsed or opened.
The package index files are corrupted
Such messages usually don't go away for quite a long time, and may prevent legitimate updates from installing.
This usually happens even more frequently if using a proxy to access apt archives.
While I don't know what's the root problem, I've got a quick workaround that seems to fix the immediate error:
sudo -s -H bash -c 'apt-get clean && rm -f /var/lib/apt/lists/* ; rm -f /var/lib/apt/lists/partial/* && apt-get clean && apt-get update'