Google has traded blows with a group of rivals including Facebook and Twitter as each side tries to seize the moral high ground in the increasingly bitter online social networking wars.

On Monday, Google came under fresh attack over controversial changes made to its search engine earlier this month that critics claim were designed mainly to divert traffic to its new social network, at the cost of devaluing its search results.

Facebook and Twitter, backed by MySpace and other unnamed allies, released an optional online tool designed to strip Google+ listings from Google search results, instead replacing them with listings from social sites that claim greater user interest.

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The search company's enemies also sought to turn Google's famous promise to remain ethically pure against it, dubbing their new tool "Don't be Evil." Google refused to comment on the new weapon in the social networking wars, which was released on a website called Focusontheuser.org.

The battle over Google+ has turned increasingly ferocious as Google has thrown the weight of its dominant search engine behind the service. The social network reached 90 million users this month, more than twice the number of three months ago, with 80 per cent visiting at least once a week, according to Google.

The search company won plaudits from human rights groups as it announced a policy change on Monday on its Google+ network that will make it easier for users to appear under pseudonyms. The more lenient approach contrasts with Facebook's insistence on the use of "real names," which activists claim exposes political dissidents to reprisals in some countries.

Google's relaxation of its names policy is a "positive development" that "challenges the notion that social networks can't allow pseudonyms without undermining the user experience," said Arvind Ganesan of Human Rights Watch.

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Jillian York of the Electronic Frontier Foundation also said Google had gone much further than Facebook in trying to deal with the human rights concerns raised by its identity policies, though she also said that some users who tried to disguise their real names while setting up accounts might still encounter problems with Google's appeals process.

Facebook continues to insist that users appear under their real names, though it has often turned a blind eye to transgressions. However, activists say this exposes dissidents to being thrown off the network at critical moments, since their enemies can prompt Facebook to act by lodging carefully timed complaints.