How to find a text file which contains a specific word inside (not in its name) in Ubuntu 12.04

I want to find a text file in my hard disk which contains a specific word. I want to use a graphic application. 

Prior to Ubuntu 12.04 I used to start in the dash an application, I think it was called "Search for file...", whose icon was a magnifying glass. 

In Ubuntu 12.04 :

Install gnome-search-tool.

Open Search for files select Select More Options and

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