Online user groups have seized power from vendors and are increasingly calling all the shots, according to Gartner research director Steve Prentice.

He warned vendors they need to rethink how they exploit users for marketing purposes. "These communities provide a strange and implicit trust between anonymous users," Prentice added.

While vendors can use these communities as a support centre, Prentice warned they risk savage retaliation and bad publicity if marketing is surreptitiously introduced.

"These communities are very strange entities as users will go out of their way to help someone they have never seen before and this advice is trusted without question - and in most cases, rightly so," Prentice said, adding that users aim to present accurate information in order to build online reputations.

"While we are seeing businesses successfully leverage these user groups as support centres for their products, I know of some scalps that the groups have claimed as a result of sly sales pitches slipped into a forum."

According to Prentice, the groups are an invaluable access point for customers and should be used to refine business strategy and marketing. It also provides opportunities, he said, for swift-moving vendors.