Brand stalker cometh?

Brands have never been more vulnerable, I think. Not just because of genuine criticism that today’s Internet technology allows people to put up – and which should be welcomed by brands as feedback – but with the possibility of something that may make guerrilla marketing seem tame, there is a possibility of the arrival of professional brand stalkers’? ( I didn’t find a description to that word on Wikipedia)
In the last week or so two marketers, managing big brands, have spoken about support being garnered by a blog/ community, led by a person/group, to launch an attack on the brand with ‘malicious intent’ – I am sure it would be a challenge to even ascertain malicious intent versus genuine problem faced by a customer. Who should be believed & why?
The first marketer didn’t really deserve any sympathy and sounded dubious to begin with, but in the second instance got me thinking. Could it be that the person was very consciously stalking a brand, to gain something?
This did make me think – as blogs gain more strength, would there be a new breed of stalkers? What do marketers think? What is the legal stand? What strategies would a brand need deploy to tackle something like this?
Questions, so we could find answers!