What do these errors mean when running apt-get update on Ubuntu 15.10, and how do I fix them?

Question

ubuntu

W: Failed to fetch http://ru.archive.ubuntu.com/ubuntu/dists/wily-updates/main/source/Sources  Hash Sum mismatch

W: Failed to fetch http://ru.archive.ubuntu.com/ubuntu/dists/wily-updates/main/binary-amd64/Packages  Hash Sum mismatch

W: Failed to fetch http://ru.archive.ubuntu.com/ubuntu/dists/wily-updates/universe/binary-amd64/Packages  Hash Sum mismatch

W: Failed to fetch http://ru.archive.ubuntu.com/ubuntu/dists/wily-updates/main/binary-i386/Packages  Hash Sum mismatch

W: Failed to fetch http://ru.archive.ubuntu.com/ubuntu/dists/wily-updates/universe/binary-i386/Packages  Hash Sum mismatch

E: Some index files failed to download. They have been ignored, or old ones used instead.

The contents of the file with the list of repositories:

cat /etc/apt/sources.list
# deb cdrom:[Ubuntu 15.10 _Wily Werewolf_ - Release amd64 (20151021)]/ wily main restricted
# deb http://ppa.launchpad.net trusty/main i386 Packages
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://ru.archive.ubuntu.com/ubuntu/ wily main restricted
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://ru.archive.ubuntu.com/ubuntu/ wily-updates main restricted
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://ru.archive.ubuntu.com/ubuntu/ wily universe
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily universe
deb http://ru.archive.ubuntu.com/ubuntu/ wily-updates universe
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily-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.
deb http://ru.archive.ubuntu.com/ubuntu/ wily multiverse
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily multiverse
deb http://ru.archive.ubuntu.com/ubuntu/ wily-updates multiverse
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily-updates multiverse

## 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://ru.archive.ubuntu.com/ubuntu/ wily-backports main restricted universe multiverse
deb-src http://ru.archive.ubuntu.com/ubuntu/ wily-backports main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu wily-security main restricted
deb-src http://security.ubuntu.com/ubuntu wily-security main restricted
deb http://security.ubuntu.com/ubuntu wily-security universe
deb-src http://security.ubuntu.com/ubuntu wily-security universe
deb http://security.ubuntu.com/ubuntu wily-security multiverse
deb-src http://security.ubuntu.com/ubuntu wily-security 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 wily partner
# deb-src http://archive.canonical.com/ubuntu wily partner

Answer 1

rm `find /var/lib/apt/lists -type f`; apt-get update