On Tuesday, May 27, 2008 an unpatched (at time of writing) 0-day vulnerability was discovered in Adobes Flash Player.

This attack is known to be in the wild and a large number(20,000+) of websites have been injected with exploit code to infect users who visit them.

More information about the exploit is available at the Security Focus website. Adobe is aware of the exploit and are working on a fix but until it is released be very careful of untrusted sites and links from unknown origin.