You can obfuscate vbs files or convert them into executables.
I know only commercial tools for the conversion to exe.
For the obfuscation
screnc.exe is a free encoder/obfuscator from Microsoft
(you can search for other tools)
The obfuscated vbs files are quite always detected by antivirus software as suspicious/malicious.
All the obfuscated files, independently of the tool that you use, can be easily deobfuscated
ref:
http://www.interclasse.com/scripts/decovbe.phphttp://isc.sans.org/diary.html?storyid=3351