Filtering javascript injection

Hello there,
one of our sites has been hacked with javascript redirection code injected in the wp_posts.post_content table field. We successfully removed it. However, I’m looking for a solution able to block such attacks (I’m already using a firewall plugin that seems to let this type of attack through at the moment).
As any executable javascript code is unwanted in a post, my thought is to filter out the sql statement needed for such an attack. I think the statement to filter out would look something like
"update wp_posts set post_content=xyz<script ...></script>"
So my question is: would your plugin block such an attack?
Thank you.
Best, Larry.