They are using a browser add-on called ‘Don’t be evil’ (a reference to one of Google’s early mottos), to stop Google from promoting its own social network, Google+, to the top of people’s web searches.

The Facebook, Twitter and MySpace campaign follows the launch of a Google search update called ‘Search Plus Your World’, which means users will see more links to Google+ when searching the web, including in part of the results page set aside for advertising.

Google’s promotion of its secondary services via search is considered a monopoly abuse, and is being in investigated by European competition authorities.

Google said in a blog post: “You can find relevant Google+ posts from friends talking about an amazing trip they just took, whether they’ve shared privately with you or publicly.

“Starting today, if you search for a topic like [music] or [baseball], you might see prominent people who frequently discuss this topic on Google+ appearing on the right-hand side of the results page.”

Twitter’s most senior lawyer, Alex Macgillivray, branded the launch a “bad day for the internet” and accused Google of “warping” search.

Twitter and Google have engaged in a war of words over ‘Your World’, with Twitter, saying it would make it hard for internet users to find relevant tweets to their search.

Twitter issued a press release saying: “For years, people have relied on Google to deliver the most relevant results anytime they wanted to find something on the Internet.

“Often, they want to know more about world events and breaking news. Twitter has emerged as a vital source of this real-time information, with more than 100 million users sending 250 million Tweets every day on virtually every topic. As we’ve seen time and time again, news breaks first on Twitter; as a result, Twitter accounts and Tweets are often the most relevant results.

“We’re concerned that as a result of Google’s changes, finding this information will be much harder for everyone. We think that’s bad for people, publishers, news organizations and Twitter users.”

Google responded via Google+, accusing Twitter of hypocrisy.

Google said it was “a bit surprised by Twitter’s comments about search plus Your World, because they chose not to renew their agreement with us last summer”.

The retaliation referred to Twitter’s refusal to allow Google to fully index tweets because it would agree to its terms. In October, its chief executive, Dick Costolo, told The Telegraph “we just can’t agree on what the appropriate value exchange is”.

Twitter does have a deal with Microsoft to allow Bing, Google’s biggest search engine rival, to index tweets.

The Google update is only live in the US at the moment.

The Twitter, Facebook and MySpace-developed ‘Don’t be evil’ browser add-on, will negate the effects of the latest Google update.

The software can be downloaded from