Drupal 7 provides a feature that allows you to install a new module via the Drupal interface itself, without entering your hosting server's cPanel/alternative File Manager to upload files.
That works like a charm for most hosting servers and makes installing modules/themes a breeze on Drupal.
For some others, trying to install modules that way (from admin/modules/install) might just bring up something that looks like the following:
Exception: Invalid checksum for file ... calculated, 0 expected in Archive_Tar->_error() (line 635 of .../my-site.com/modules/system/system.tar.inc).
Here's how to fix this: