Twitter users who thought friends were directing them to a "funny blog" got caught up in a phishing scam.

The microblogging service was hit by two different rounds of phishing, as criminals tried to take control of user accounts and then use them as a springboard to attack others.

Both Twitter and Facebook have been hit with phishing attacks in recent days. "The social networking attacks are becoming increasingly common," said Jamie De Guerre, chief technology officer with anti-spam vendor Cloudmark. "Spammers are really moving to attack social networks because of the popularity of the social networks and also because they're not as well defended as most e-mail platforms."

Twitter was hit by another high-profile phishing attack in January. This latest attack had snagged several hundred victims by mid-day yesterday.

Yesterday's attack worked by hackers creating fake Twitter accounts and then started following legitimate Twitter users. Twitter notifies users when they have new followers, sending the user a link to the follower's Twitter profile page. In this case, the profile page contained a link to a phishing site. So the victim, while investigating his new follower, would end up on the fake site Tvviter(.)com (this page is not safe to visit) where he would be asked to enter his Twitter username and password.

Once the phishers obtained their victim's login credentials, they used them to launch the second round of attacks. In this round, they posted Twitter messages such as "hey check thiss out" or "Hey. there is this funny blog going around." These messages included a link to another phishing site.

Scammers are phishing social networks because they have a better chance of tricking their victims, said Rik Ferguson, a security researcher with Trend Micro in his blog about the latest phishing campaign. They "tend to be more successful, because they take advantage of the inherent trust that these systems are based on," he said.

Once criminals have access to these accounts they can make money by sending out spam messages via Twitter or Facebook, or they can re-use the username and password combinations to try to log into other services such as web-based email, Ferguson said.

On Thursday, security vendor AppRiver reported a new round of Facebook phishing attacks. These messages have the subject line "Hello" and read "Check areps(.)at." This scam, which tries to steal Facebook usernames and login credentials, also promotes the bests(.)at domain. (These domains are also unsafe to visit)

Another reason why Twitter spam is so effective is because Twitter users rarely know what sites they're going to visit. Because messages can't be more than 140 characters long, senders often use services like TinyURL or UR.LC to shorten their links, hiding the ultimate destination from web surfers until they arrive at the site.