I updated this plugin and it wrecked my site as follows:
I logged into my Wordpress Dashboard on melvichestamps.com, tried to up some plugins which appeared to be successful. Tried to update the theme but this didn't work. Exited and tried to access the dashboard again, but I didn't even get to the sign in page. I got this message instead:

"Warning: require_once(/home/candj803/public_html/melvichestamps.com/wp-content/plugins/wpmu-dev-plusone/lib/external/google/contrib/Google_plusService.php) [function.require-once]: failed to open stream: No such file or directory in /home/candj803/public_html/melvichestamps.com/wp-content/plugins/wpmu-dev-plusone/lib/class_wdgpo_google_auth.php on line 444

Fatal error: require_once() [function.require]: Failed opening required '/home/candj803/public_html/melvichestamps.com/wp-content/plugins/wpmu-dev-plusone/lib/external/google/contrib/Google_plusService.php' (include_path='/home/candj803/public_html/melvichestamps.com/wp-content/plugins/wpmu-dev-plusone/lib/external/google:.:disappointed:usr/lib/php:disappointed:usr/local/lib/php') in /home/candj803/public_html/melvichestamps.com/wp-content/plugins/wpmu-dev-plusone/lib/class_wdgpo_google_auth.php on line 444."

The good folk at Hostgator restored it as follows:
Thank you for contacting HostGator.

I sincerely apologize for the inconvenience. This is not an issue with sitelock, however this does appear to be caused by one of the plugins which you uploaded. It would appear that the plugin "wpmu-dev-plusone" is causing issues which is preventing your site from resolving. I have disabled this by backing up that directory (now wpmu-dev-plusone-bak/) and your site is resolving without issue.

Please do not hesitate to contact us if we may be of any further assistance.
Bradley H
Linux Administrator
HostGator, LLC.

This plugin is now deactivated and I'm of a mind to remove it completely. To up-date it I simply clicked on the "update" button. It didn't seem to work even though the other plugins updated.
Could you please shed some light on this problem before I do anything else.

Thank you

John Melville.