The Incoming Links widget in WordPress Dashboard allows you to customize and configure the number of inbound links that you want to display in the Dashboard. However, the default configuration of Incoming links is 10. but you can display the number of incoming links upto 20.
Many of you are aware that WordPress has been using Google Blog Search as the search engine to provide such information on incoming links.
For example ( Incoming link of the Windows Club Blog):
link:http://www.thewindowsclub.com/ - Google Blog Search
Source: Know Incoming links of any Blog