How to write code to search for a desired string in external independent excels files

I want to have a command button in an independent excel worksheet which will execute a macro which in turn would search for a particular text string such as “Error” within a selection of independent excel files residing in a local directory such as C:\ and return a Pass/Fail value when it finds such a string in the collection of excel files.

Example:
Command button Cmd_1 in “Sheet1” of an excel sheet (template) will fire a macro to search for a text string such as “Error” in two independent files (Data1.xls, Data2.xls) and return True/False depending upon whether the string “Error” is found in either of them.

How do I come up with a code for the above? What search functions could I use?

Thanks