My banners are blocked by "[AD]" message

This is a strange problem and I would be most grateful for any assistance.

I am unable to remove what seems to be an ad blocking program from my PC, running Windows XP. On many pages, instead of an image there is simply the word "[AD]" (AD in square brackets) in the middle of the image frame. Normally this wouldn't bother me and I'd consider it a blessing not to be bothered by popups and ads, but I created a website using .jpg images as banners (a different one for each page), and now find they are also replaced by "[AD]" when I view them online. This occurs in Firefox, IE and Seamonkey.

(I have a vague recollection, a couple of years ago, of installing some ad blocking program that may have done this, but I can't remember any more details than that.)

When I view the original website (my own working copy on my HD), there's no problem and the images display fine.

What's more puzzling is that the computer in the room next door (running Vista) does not have this problem at all! The page banners are visible, online. No special popup blockers are installed and Avira and Zonealarm free versions are installed on it. Both are on the same network and use the same ISP.

I thought at first that AdBlock (Plus?) might be responsible but the problem persisted after it was uninstalled. Since I did not install any popup blockers on IE, this blocking of banners is obviously a system-wide thing.

The banners are stored in the subdirectory 'bnr' (banner) of 'img' (images), so that the HTML reads

<img src="img/bnr/home_bnr.jpg" width="620" height="55" border="0" alt="home banner">

However, when I upload the website, I discover that when viewed in View Page Source, on **my** computer, the image code has been replaced by

<FONT size="1">[AD]</FONT>

Note the change to upper case. This could mean that either the image is missing or maybe something is trying to replace it with an ad or thinks it's an ad.

Crazy as this may seem, it all seems to hinge on the fact that the banners are located in a directory named "bnr". If I change the name to anything else, such as "banr", "bna" or "banner", the problem goes away. And it happens **only on my machine**.

Submitting the URL to browsershots.org displays it ok.

So what could cause it? If I replace the image code with text, that displays ok. I've deleted the whole website and re-uploaded it, with no improvement. I've rebooted in safe mode, run Firefox in safe mode, turned off all my antivirus & antispyware, etc (Ad-Aware, Avast antivirus and Agnitum Outpost Firewall), and still the same problem. Antivirus checks show nothing suspicious.

I guess I could wipe my HD, reinstall Windows XP and start all over again, but I'd rather not!

Thanks for any suggestions. I've tried turning off every application likely to be causing this, cleaning the Registry, etc., without success. Unless I can find the reason for this it will continue to plague me as a web developer. I suspect the cause is something simple, but have had no luck so far.

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I've read your Windows XP Cleaning Procedure web page and I have run CCleaner. Apart from this problem, my PC runs cleanly and nothing else points to a virus, so I'm crossing my fingers that the cause is simple enough for me to fix without having to resort to HijackThis logs, etc.

I've also posted this request for help here:
http://webdeveloper.com/forum/showthread.php?t=223915

So far there have been no replies.

 

No, it wasn't malware, though I did check for it.

I had installed Agnitum Outpost Firewall Pro, which (by default?) has three ways of preventing ads and other images from being displayed in your browser:

1. "Graphics and advertising that contain any of the listed keywords are
removed by Outpost Firewall Pro before the page is displayed in the
web browser."

2. "Any graphics or advertising image that matches a size on the list will be
blocked by Outpost Firewall Pro before the web page is displayed."

3. "Use ImproveNet ads keyword list:
This updatable list is provided by ImproveNet service. Graphics and
advertising that contain any of the listed keywords are removed by Outpost
Firewall Pro BEFORE (capitals mine) the page is displayed in the web browser."

THIS was my problem. The list includes:
* /bn.*
*/bnr/*
*/bnrs/*

A warning to all.