Researchers recently launched a free spam-filtering service for Twitter that flags offenders for the microblogging service, which, in turn, removes the offending accounts.

The Spamdetector service crawls Twitter, using heuristics to detect spam accounts. Gianluca Stringhini, the researcher heading up the service, says the tool has a low false-positive rate.

"Around a year ago, we started observing these [social] networks, looking for malicious traffic...spammers show a very different behavior compared to real users, and therefore we were able to build a system that can detect them in a reliable way," says Stringhini, a researcher at the University of California-Santa Barbara.

Twitter already offers its users a button for reporting possible spam, but it relies on the user to spot suspicious tweets. The social network last week also added a new service that detects malicious URLs in an effort to quell the rise in spam and phishing on the network. It ultimately will scan all URLs before they hit the Twitter feed, but initially is doing so only for URLs sent via Twitter direct messages [DMs] and email notifications about DMs.

To be sure, abuse on Twitter is on the rise: One in eight Twitter accounts was found to be suspicious, malicious, or suspended last year, according to a recent report from Barracuda Networks. And Twitter itself currently finds 3 to 4 percent of accounts to be malicious, according to Barracuda's data.

Spamdetector also takes potential spam submissions from users who want to check if a tweet is legitimate. "Our system crawls Twitter on its own, and the spam detection happens mostly without users' submissions. We ask users to flag spammers to us because, in this way, we can target the crawling to certain accounts -- for instance, those sending tweets that have been detected as spammers -- allowing us to detect more spammers in a shorter period of time," Stringhini says. "When we detect spammers, we flag them to Twitter, which then takes care of deleting them."

Spamdetector profiles spammers based on features that are common in spammer accounts. "For example, spammers usually follow a large number of profiles, but are followed back only by a small fraction of them. They also usually send out very similar messages," Stringhini says. "We calculate some ratios related to the defined features for each account and flag as spammers those profiles that exceed a certain amount of thresholds in those ratios."

David Maynor, CTO of Errata Security, which runs an experimental service for detecting Twitter spam and threats called TwiGUARD, says spam has grown 3 percent since TwiGUARD first launched in September.

TwiGUARD was one of the first security tools for Twitter. It uses a reputation-based algorithm to see if a follower is a spammer or if a link is infected. The service also analyzes malware found via tweets. Maynor says Errata could eventually offer TwiGUARD as a full-blown service. "We're fine-tuning the algorithms for developing a user-friendly front-end to it," he says.

UC-Santa Barbara's Stringhini, meanwhile, says Twitter is actively fighting spam and malicious accounts on its network. "It is not easy to detect malicious accounts among millions of users. Moreover, Twitter is peculiar because many legitimate accounts are managed in an automated fashion, [such as] profiles of shops and posting deals, and this might lead to a wrong detection," he says. But Twitter is having some success on its own -- some have already been suspended when Spamdetector has flagged them, for example, he says.

As of Tuesday, the new service had detected -- and removed -- nearly 3,400 spam bot accounts in about a month.

To get the Spamdetector services, just follow @spamdetector on Twitter.

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