SPUG: Web Bugs

Ken McGlothlen mcglk at artlogix.com
Mon Aug 20 20:05:18 CDT 2001

Doug Beaver <doug at beaver.net> writes:

| What is it about transparent gifs (whether they are static or generated by a
| cgi) that makes it easier to log and retrieve page view data?  I am trying to
| see the benefit, but I can't.  Can you explain a little more?

Specifically, when you visit a site (say, cnn.com), they have the option of
dropping in a webbug (or set of them) from various other firms.  The cnn.com
page might consist of:

        The HTML document
        An IBM ad
        A Compaq ad
        A doubleclick.com webbug

The doubleclick.com webbug almost always has a way of encoding more information
in the URL, so now doubleclick.com knows that you saw the article, which ads
you saw, and when you saw it.  They also work with cnn.com to discover the
referring URL.

Alone, this is no big deal, but you can see how, with enough webbugs on enough
sites (and it doesn't take a majority of them), doubleclick.com can come up
with a really good profile of individual users, and come up with more effective
(read "obnoxious") advertising tactics.

Even worse is emails---it's like a read-receipt that mailreaders like Outlook
won't let you block.  This is one of the primary reasons why I don't use a
graphical mailreader.

| The thing that upsets me about web bugs is that you can't turn them off.  At
| least you can turn off cookies.  Even if you're using a proxy which strips
| your identifying headers, they can still track you since the tracking info is
| encoded in the image name.

Well, there are ways.  On the Macintosh, for example, a popular web-browser
named OmniWeb allows you to do URL blocking (with regular expressions, no
less), and that one ability (along with superior cookie management) has made it
my favorite browser.  Mozilla is also going to permit you to block images from
sites, whenever it becomes ready for prime-time.  Your only other avenues are
HTML proxies like junkbuster, which block image requests from sites you select.

| You might be able to test for the existence of web bugs by using a proxy
| and doing a HEAD request on each "image" referred to by <img> tags.

Actually, if you can just get a list of IMG URLs out of the page efficiently,
they're pretty easy to spot.  OmniWeb has the "Get Info" command; it will list
all the resources a page attempts to load.  But it does take a pair of eyeballs
to distinguish ads and webbugs from legitimate spacers and the like.

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