Vivid apt-get update huge Package files in /var/lib/apt/lists/partial

Sounds a bit like a proxy problem. I once had a problem with maven that the proxy replaced a jar by a html page containing a virus warning. The html got saved as .jar but because it was broken nothing worked anymore.

Anyway: it's safe to delete everything from the directory /var/lib/apt/lists/partial/ (and also from /var/cache/apt/archives/partial/).

For troubleshooting, I recommend the following steps:

• Try another mirror, eg. http://de.archive.ubuntu.com/ubuntu/ instead of http://ch.archive.ubuntu.com/ubuntu/ or even the main archive http://archive.ubuntu.com/ubuntu/
• Try another protocol: ftp:// instead of http:// - the rest of the path remains for default mirrors
• Try to analyze the transfer using wireshark (use the context menu option 'Follow TCP stream'). Interesting are both HTTP headers and content. If you get answers with HTTP status code 200 (which means ok) but human-readable content, something is seriously wrong on your proxy. A regular bzip2 file shouldn't contain any human-readable text.
• Use wget or curl for checking what you get from the server when downloading without apt-get.