NEW YORK (CNNMoney) -- Twitter is cracking down on spammers.
The company on Thursday filed a lawsuit in federal court in San Francisco against five of its most aggressive spam enablers.
The defendants include JL4 Web Solutions, based in the Philippines and referred to in the suit as "TweetAttacks." Other defendants include Tennessee-based Skootle Corporation, referred to as "TweetAdder"; "TweetBuddy"; and the individuals James Lucero and Garland Harris.
The lawsuit takes aim at the people building spamming tools, such as software that latches on to trending topics and starts injecting irrelevant marketing messages into the mix.
"With this suit, we're going straight to the source. By shutting down tool providers, we will prevent other spammers from having these services at their disposal," Twitter said in a blog post. "Further, we hope the suit acts as a deterrent to other spammers, demonstrating the strength of our commitment to keep them off Twitter."
By Friday afternoon, several of the websites named in Twitter's suit -- TweetAttacks, TweetBuddy, and a site operated by Lucero -- were offline. TweetAdder's site was still running, as were several of Harris' sites. The site operators could not immediately be reached for comment.
Twitter says it has spent around $700,000 in anti-spam efforts to combat the defendants' marketing blitzkrieg. It is seeking injunctions against each defendant as well as monetary damages.
Twitter is starting to take its spam problem -- a longtime annoyance -- more seriously. In January, the company acquired Internet security company Dasient, a deal aimed at bringing in new technology to fight off spammers.
Performics, a company that monitors its clients' brands on social platforms, says it sees significantly more spam on Twitter than on Google and Facebook.
"You have to eliminate all the irrelevant content to see what people are really saying," said spokesman Dan Malachowski. "On Twitter, a lot of it is irrelevant spam."
Twitter said on its blog that its engineers have recently launched new anti-spam measures "to more aggressively suspend a new type of @ mention spam." The company is also using its t.co link shortener as a defense: It tracks what's tweeted and tries to shut down links to malware or malicious content.
According to PeekYou, a search company that monitors Twitter's spam levels, the efforts are noticeable.
"Twitter has gotten a lot better over the last six months," CEO Michael Hussey said. "I think they're more quickly detecting and deleting lots of spam."
But it's still pretty far from perfect.
"You can go on eBay today and type 'twitter followers' or 'buy twitter followers,' and you can pump up your number," Hussey said. "Those are great examples of completely spam accounts." 
