A service that targets Twitter users for marketing messages is reining in spammers as advertisers strive to take advantage of the popular micro-blogging network.

TwitterHawk is limiting marketers to sending only a single message each to any particular Twitter user every six hours, according to a message at the firm's website on Monday.

TwitterHawk runs a service that scours Twitter messages for key words and then fires off missives that are essentially advertisements targeted in a manner similar to Google matching online ads to search queries.

For example, the operators of a coffee shop could use TwitterHawk to pinpoint local Twitter users who mention coffee in "tweets" and then send them messages inviting them to try the cafe.

"The system will spread out your replies so they look more natural, and rotate through your different responses so it doesn't appear repetitive when people view your account," TwitterHawk promises.

"We can even add the user we find as a friend on Twitter for you to give you that extra little edge."

TwitterHawk owner Chris Duell said in an online statement the service was not intended to be a weapon for spammers to bury Twitter users in hails of unwanted pitches.

"We do not in any way condone using TwitterHawk for aggressive SPAM based marketing tactics to harass or annoy people with advertising material on a regular basis," Duell wrote.

"We view this in the same way that Google Adwords provides non intrusive offers to users based on the keywords they told Google about -- but without this being forced upon them or annoying them."

Backlash from Twitter users inspired TwitterHawk to restrict how often marketing messages can be sent and promise that tougher controls will be implemented if the service causes "unwanted problems."

"We did not expect such an explosion in use of the tool and considerably underestimated its effect on the social medium," Duell wrote.

Twitter has yet to start making money from the fast-growing service that encourages users to share what they are doing at any given moment in the form of terse haiku-style text messages on mobile phones.

The California-based firm doggedly works to thwart spammers, marketers, frauds, and criminals from exploiting the service and its millions of users.

Twitter vigilantly deletes accounts of suspected spammers or fraudsters.

On Monday, it suspended an account said to have been set up the Tibetan spiritual leader the Dalai Lama saying it had been created by an impostor.