Webpage Update Notification

Webpage Update Notification
-- An advanced checker to notify changes occurred between visit

I would like to have a program which can keep track of different webpage. When the pages change, there is an alert/popup which will notify me. It is useful to track changes like new replies in particular boards, site news, version update news etc.

However the problem is a single unrelated change in a page would trigger the notification. For example, a random ad in the forum which will always trigger the alert. I wonder if the check can be more advanced. For example:

• alert only when the selected part of the webpage is updated
• decide the threshold on how many changes are needed to trigger the alert (helpful to prevent small unrelated changes from mis-triggering)

Do you have any program you can recommend?
I can pay for the program as long as it is powerful and suit my needs.

A program using wget and string searches would probably work, the creation would take some time.

Some scripting would be able to do that. Use the GET method with the additional header If-Modified-Since:. That would indicate a change in the page itself (and not any linked pages or any other inserted page like ads).

Perl in combination with libwww (LWP modules) will make short work of this.

There are also the tools that the website management software provides?

1. Subscribe to threads
2. E-mail notification
3. New Posts
4. Today's Posts

I would also advise a little caution as some websites don't like you using external "tools" on them?