this "virus" is very simple to counteract, assuming you are running a pattern matching capable MTA (Mail Transmission Authority). in your mail delivery program like sendmail, postfix or whatever you need to point it to use procmail by default to filter all messages. once you have done that, add this line to /etc/procmailrc:
:0
* ^Subject: ILOVEYOU$
EXITCODE=67

this will bounce anything sent through that mail server, both incoming and outgoing messages.
hasta la vista, stupid macro virus!