Prevent a plugin from running bassed on url/script

[h2ojunkie]

I've been working with a plugin that runs on attachment.php at the attachment_start hook.

I'm looking for a way to prevent this plugin from executing when a user is viewing showthread.php or showpost.php.

For example, a user embeds a attachment image in a post using "" I don't want the plugin to run.

I've tried using a this_script conditional to check for showthread or showpost, however that isn't working. I'm not an expert at this, but my assumption is this_script won't work because even though they are viewing showthread, attachment.php is still called in the link which makes this_script = attachment.

Can anyone suggest another way to prevent the plugin from running in this situation?

Thanks in advance!