The capitalization is important to most popular search engines, including Google (source). Change your file name from Robots.txt
to robots.txt
. If you name it correctly, most popular search engines (Bing, Yahoo, Google, etc.) will not index it. No extra effort on your part.
Here is Yahoo's crawler help that describes case-sensitivity.
Here is the standard that describes common courtesy for crawlers with regards to robots.txt. It is explicitly stated that empty robots.txt files are ignored completely, and it is common sense that they are not indexed. Otherwise, we would see billions of robots.txt search results in Google.