Phishing scams have become increasingly common on social networking sites as scammers have become savvier and bolder in their attacks, according to GFI Software.

In recent months, scammers have used surveys, competitions and the promise of adult content to entice Internet users into divulging their personal information, said GFI Software which has announced the top 10 most prevalent malware threats for June 2011.

The top ten malware threats are: Trojan.Win32. (29.78%), Zugo Ltd (2.37%), INF.Autorun (1.59% ), Exploit.PDF-JS. (1.41%), Trojan.Win32.Jpgiframe (1.39%), Trojan.JS.Redirector.cd (1.32%), Trojan-Spy.Win32.Zbot.gen (1.20%), Pinball Corporation.(1.13%), Adware.Win32.(1.12%), and GameVance Adware (1.07%).

The company said that in June the most important phishing attack was that in microblogging site Tumblr, which compromised up to 8,000 user accounts.

Additionally, June saw scammers distributing rogue antivirus software by taking advantage of search traffic related to popular Pokemon video games, as well as luring users to fill out seemingly endless fake questionnaires, said the company.

GFI Software senior threat researcher Chris Boyd said, "The Tumblr phishing and spam attacks highlight the importance of building greater awareness about online threats and simple tactics we can all use to defend ourselves."

"Some of the attacks we saw in June were aimed at compromising social networking login credentials knowing that many people still use the same username and password for all their online activities, including banking, shopping and email.

It is important for users on any social networking site to approach content that looks out of place with care since, as seen on Tumblr, seemingly innocuous attacks can evolve into more serious threats. Also, strengthen your passwords and vary them across all your online accounts to limit your risk and exposure if one is compromised."