It's the Internet's oldest cliche, that online no one knows I'm a dog. But what was once a playful jibe about the Web dating scene has taken on a darker timbre.

On the side of the angels we have The Yes Men (theyesmen.org), who indulge in what they call 'identity correction'. 'Honest people impersonate big-time criminals in order to publicly humiliate them. Targets are leaders and big corporations who put profits ahead of everything else.'

Their tactic of choice is the 'funhouse mirror' corporate Web site. This looks virtually identical to the true site and has a credible URL, but the text is a subtle (and sometimes not so subtle) spoof of the corporate site it's aping. The Yes Men's spoof of Dow Chemical's corporate site attracted huge publicity last year, none of it good as far as Dow was concerned.

The Yes Men didn't stop there. Their Reamweaver site (http://reamweaver.com) provides a quick and easy production tool that allows anyone to create their own funhouse mirror site. I don't know how many people have made use of this tool, but Burson-Marsteller knows of at least one: a US student called Paul Hardwin, who saw one of the Yes Men's parodies and decided to create one of his own, using the Burson-Marsteller corporate site.

Both Dow and Burson decided to adopt a high-handed attitude to the sites and shut them down, a tactic that simply made matters worse and added to the damage.

Philosophically, the Yes Men argue they're warping the image projected by corporate sites to create a more accurate account. It's manipulation, but is it deception if it aims to tell the truth?

On the side of the less than angelic, some companies are manipulating the medium to tell their own version of the truth.

Sites like foodsecurity.net and junkscience.com purport to be independent platforms run by individuals who are concerned about media manipulation of issues like genetic modification.

It turns out, when you do a little digging, that Foodsecurity was created by the Bivings Group, an Internet PR company that numbers Monsanto among it clients, while Junkscience is run by Steve Milloy, a long-time political lobbyist for industry.It's an ironic twist that while the inter-activists are aping corporate sites to make their political points, the corporations are posing as activists to push theirs. That's a lot of distortion.

The difference is that the activists don't intend us to be deceived by their funhouse mirror sites: if we are, they've failed. The pseudo-activist sites, on the other hand, explicitly promote themselves as something they're not: disinterested parties with no money in the game.

This is a blinkered tactic that erodes long-term value to make a short-term gain. It might work for a little while, and even help the companies which sponsor such ventures win an argument or two, but there's a bitter paradox nestling inside the candy exterior of this little pill.

The more successful the strategy in the short term, the more it will eventually corrode trust in the long. People persuaded by such sites will feel betrayed when it becomes evident they were duped. And it won't even matter if the pseudo sites have truth on their side: when a messenger is exposed as an impostor, their credibility is destroyed.

Why are companies sponsoring this form of online deception in the first place? Because they've lost all credibility with the general public. Trust of corporations is at an all-time low and everything they say is viewed with suspicion, so they have to create 'unbiased' third parties to speak on their behalf, to give their message any hope of being believed. In doing so they're driving distrust a layer deeper; indeed, they risk destroying what little credibility the online medium has as a whole.

Once you realise that some of the people out there on the Internet really are dogs, you begin to suspect that everyone may be.

Phil Dwyer CEO of C-Infinity Research.