Background:
The Windows Script Encoder (screnc.exe) is a "Microsoft tool which can be used to encode your scripts (i.e. JScript, ASP pages, VBScript)". By using this tool, you can prevent people from looking at, or modifying, your scripts. Microsoft recommends using the Script Encoder to obfuscate your ASP pages, so in case your server is compromised the hacker would be unable to find out how your ASP applications work.
Windows Script Decoder is a tool that can decode all scripts that have been encoded with the Windows Script Encoder.