"apt-get update" Hash Sum mismatch

[linux unix]

When I use "apt-get update" command,I get the results like "W: Failed
to fetch bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_saucy_main_binary-amd64_Packages
 Hash Sum mismatch" "W: Failed to fetch
bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_saucy-updates_restricted_binary-i386_Packages
 Hash Sum mismatch" "W: Failed to fetch
bzip2:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_saucy-updates_restricted_binary-i386_Packages
 Hash Sum mismatch".Though I have ever changed the package sources and
run "rm -rf /var/lib/apt/lists/*",it always appears.I have met these
problems never ever,and I have met a few days like these.So I want to
know what is the problem? Could anyone meet the same problems?(Ubuntu
13.10 amd64)