As the Sophos security blog reports, attackers are now using offers of "Free Farmville Secrets E-books" as the bait to attract the clicks necessary to activate the scam. Other popular bait subjects include Sex and the City 2, Shrek, bp, free gift cards, UFC and "sexy videos."
How can you protect yourself? Basically the best way is to be careful about what links you click, and to monitor your personal wall posts for any unsolicited messages (you can delete them if you notice them). We hope Facebook will take steps to close this security hole soon, but until then, eternal vigilance is the price of liberty.