Facebook and the state of Washington sued a company on Thursday they accused of a practice called clickjacking that fools users of the world's top social network into visiting advertising sites, divulging personal information and spreading the scam to friends.

The scheme, also known as likejacking because victims are tricked into using Facebook's Like button to perpetuate it, has grossed $1.2 million a month for the Delaware-based firm, Adscend Media, according to the state attorney general's office.

Adscend profits from the scam by collecting money from its advertising clients for every Facebook user unwittingly misdirected to a target ad or subscription service, the plaintiffs said.

Two separate but similar claims filed in federal court by the state and Facebook accuse Adscend of violating federal and state statutes outlawing misleading or deceptive commercial electronic communications and unfair business practices.

The legal action is believed to mark the first time any state government has gone to court in a crackdown against spam spread by Facebook, the world's most widely used social media network, said Paula Selis, senior counsel for the attorney general.

She said schemes such as clickjacking have grown steadily more pervasive, and that millions of Facebook users have probably been exposed to Adscend's spam.

Security is an arms race, Ted Ullyot, Facebook's general counsel, told a news conference at the California-based company's Seattle office to announce the lawsuits. It's important to stay a step ahead against spammers and scammers.

Attorney General Rob McKenna, a Republican running for governor, said Washington state was taking action because we've brought other cases like this and, more than any other state, we've developed technological and legal expertise in the field of cyber fraud.

Representatives of Adscend or two co-owners also named as defendants could not immediately be reached for comment.

PAGES DESIGNED AS BAIT

As described in the lawsuits, the scam works as follows:

Facebook pages designed as bait are disseminated to social network users as posts that seemingly originate from friends, offering visitors an opportunity to view salacious or provocative content.

However, that viewing is contingent on completing a series of steps that will supposedly unlock the content but are actually designed to lure Facebook users onto other sites, where they are tricked into giving away personal information or signing up for expensive mobile subscription services.

First the victims are encouraged to click the Like button on the Facebook bait page, which then alerts their friends to the page's existence, thus helping propagate it. Then they are told they cannot reach the content without filling out a form for an online survey or advertising offer.

In one example cited, the Like button is overlayed with a link labeled: This man took a picture of his face every day for 8 years! The promised content often does not exist, and the user instead is directed through a series of prompts taking them off Facebook and to a string of ads and subscription offers.

In some cases, a hidden code embedded in an enticing link on the bait page activates the Like button without the user even clicking it, sending it to friends' news feeds.

Selis said it may seem unlikely that anyone would click on such links, but unfortunately they do.

While the number of Facebook users actually scammed by clickjacking is not known, Selis said investigators have determined that some 280,000 users visited the locked content pages of Adscend during February 2011 alone.

So we know there are probably millions of Facebook users exposed to the deception, she said.

Facebook spokesman Andrew Noyes said the Adscend action was the latest in our pursuit and support for civil and criminal consequences for spammers or others who attempt to harm Facebook or the people who use our service.

He cited three federal court judgments worth several hundred million dollars each obtained by Facebook against spammers since 2008.

(Additional reporting and writing by Steve Gorman; Editing by Cynthia Johnston)

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