According to Reuters:
“Facebook’s 120 million users are being targeted by a virus dubbed “Koobface” that uses the social network’s messaging system to infect PCs, then tries to gather sensitive information such as credit card numbers…
…Koobface spreads by sending notes to friends of someone whose PC has been infected. The messages, with subject headers like, “You look just awesome in this new movie,” direct recipients to a website where they are asked to download what it claims is an update of Adobe Systems Inc’s Flash player.
If they download the software, users end up with an infected computer, which then takes users to contaminated sites when they try to use search engines from Google, Yahoo, MSN and Live.com, according McAfee.”