Firefox and the ping attribute
[Posted January 18, 2006 by corbet]
The
ping
attribute is an HTML extension proposed by the
Web Hypertext Application Technology Working
Group. This attribute may be applied to anchor ("
<A>")
tags; its value is a list of URIs. If the user clicks upon the link
created by the
<A> tag, the browser will, in addition to
displaying the destination page, also send a request for each of the given
URIs. Essentially, the browser is phoning home - possibly to multiple
homes - to report on the user's action.
As it turns out, future Firefox releases will
implement the ping attribute; by some accounts, this feature will turn
Firefox into spyware. Calling it "spyware" is probably overstating the
case a little, but this feature is still worth some thought.
Many sites perform tracking of outbound clicks now. The normal technique
is to reformat an external link to point at an internal script; that script
logs the click, then returns an HTTP "redirect" response which sends the
browser to the true destination. The redirect technique is arguably worse
than the ping attribute for a couple of reasons. The first is the fact
that redirect-style URLs obscure the true destination. Redirected URLs can
be moderately obfuscated, such as this one taken from a
News.com story:
http://dw.com.com/redir?destUrl=http%3A%2F%2Fwww.nationalskillsregistry.in&siteId=3&\
oId=2100-1029-6028107&ontId=1009&lop=nl.ex
They can also be completely obscure:
http://linuxfr.org/redirect/45255.html
(The above URL takes the reader to the Fedora directory
server page).
Redirected URLs can, in the presence of JavaScript, be imposed entirely by
stealth.
The other problem with using redirect in this way is that it requires a
conversation with the logging server before the browser wanders on to the
place the user actually wanted to be. If the logging server is
sufficiently slow or off the net entirely, the destination becomes
unreachable.
The ping attribute addresses both of these problems. Destination URLs are
not hidden, and the actual phoning home can happen after the destination
page has been displayed. The option of ignoring ping attributes can also
be presented to the user; there is no such option for links using redirect
(though there are some firefox extensions which try hard for specific
sites). So, in theory, ping is an improvement over what came before.
Still, it is hard to avoid a sense of discomfort with this feature.
Firefox is free software, and free software is written with its users'
interests in mind. Free software users have grown accustomed to the idea
that, for example, applications will not be quietly phoning home in the
background. Certainly, Firefox users have no motivation to leave ping enabled -
it potentially compromises their privacy while offering them little in
return. People will disable ping, and distributors will have a strong
motivation to disable it by default in their packages. The Firefox
hackers, by adding this feature, risk appearing to serve a community
other than their users, and that appearance could reflect back on the
reputation of this fine browser in general.
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