When creating links,​​ you should follow a few basic rules: ​

1. If your link is an internal link, then it should navigate within the same window. If the link is external, it should open in a new tab and be visually clear to the user that it will lead them away from the current site, that way it is not a surprise.
   
2. If a link is to an external site, a visual indication should be provided to the user like this: This is a link to another site.

   Search Engines (http://www.google.com is by far the best but try other search engines as well)

   Figure: Bad example - Without visual indication

   Search Engines (http://www.google.com is by far the best but try other search engines as well

   Figure: Good example - With visual indication
   

3. External link external indicators should be inserted by CSS as following:

   a[href*="//"]:not([href*="mysite.com"]):after {
       content: url(https://www.ssw.com.au/ssw/images/external.gif);
       padding-left: 4px;
   }

   Figure: Good example - Icon is added by CSS via a simple declaration
   

We have a program called SSW Code Auditor to check for this rule.