If you need to search the hard drive(s) of a Windows computer for text strings, consider installing a free application called Windows Grep, which can be found here.
Windows Grep searches plain text, binary files (including .dll and .exe files), and zip files. The strings which come up in the results can be replaced with other strings - a particularly useful feature if you need to redact information from a large set of electronic files. Once a set of files with a particular string is returned, you also have the ability to search that set for an additional string.
When searching you have the ability to either search for regular expressions, plain text, case sensitive text, or words that sound similar to the specified term. See Fig. 1.
The search tool can be set for specific file types and folders.
The search results will indicate the number of times the string appears in each file, and show where in specific files the term appears.
Note that if you use the Replace option in Windows Grep to redact the strings that come up in your search results there is an option to save the redacted version as a new file.
It's very important to emphasize that if you search for a string with multiple words, and those words appear on different lines, Windows Grep won't necessarily include the full string in the results. See a demonstration of the redaction process here: