Importance of specifying the right FileAccess option.

When debugging an application that accepts a filename as input, I came across the following exception
System.UnauthorizedAccessException: Access to the path 'C:\test.txt' is denied.

The line at which it failed was
FileStream fs = new FileStream(path, FileMode.Open);

I checked my access permissions on the file and everything was perfect. Except that I noticed that this file test.txt was marked Read Only. When I changed the above line to include the FileAccess option
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);
the code executed successfully!

So moral of this is that wherever possible we should specify the FileAccess option for file operations.