Over the last nine months or so we have received and increasing number of calls and emails from people who have experienced a sudden drop in their Google rankings.
One of the many reasons Google may deindex a site or reduce its search engine position is that the site has been flagged as being a source of malicious software.
Database driven web sites (WordPress and Joomla being the most popular), are particularly vulnerable because some themes, components and plugins are not particularly secure and hackers can alter the code on your site to distribute malicious software on their behalf.
That’s why it’s a good idea to try to minimise the number of plugins you use and try to keep your version of content management system and the associated plugins up to date.
If you want to see if your web site has been flagged by Google there is a nice tool that will let you know.
The address for this tool is http://www.google.com/safebrowsing/diagnostic?site=yourwebsite.com.au
(change the yourwebsite.com.au to your web site)
If you do see that your site has been flagged, you need to fix the vulnerability and then ask for a manual review via Google Webmaster Tools.