This is just a quick addition to the previous posting, confirming the alleged use of m_ by Microsoft in their own code.

Lutz Roeder's .NET Reflector is a fascinating tool for various reasons, including its ability to show all the .NET Framework classes that use prefixes on member variables. There are a bunch. Here is a very small sample of venerable classes that use m_:

• System.Int32
• System.String
• System.Threading.Thread
• System.Reflection.Assembly
• System.Environment
• System.Globalization.CultureInfo
• System.Net.Connection
• System.Net.HttpWebRequest
• System.Net.IPAddress
• System.Uri
• System.WeakReference

And here are a few of the classes that use a leading underscore for field names, though there aren't as many in this category:

• System.AppDomain
• System.Guid
• System.Console
• System.Exception
• System.Collections.ArrayList
• System.Delegate
• System.TimeSpan