All users who allow flash content in their browsers are at risk.
This morning we saw the first proof-of-concept exploit, which we fully expect to be the tip of the iceberg. Its likely that we'll see mass exploitation in the next few days..
To protect yourself, the best thing to do is to upgrade your flash plugin to 18.104.22.168 or later. If you use FireFox, the NoScript plugin will prevent flash content from running unless you specifically trust the source or grant it temporary permission. NoScript can be annoying, but its an extremely valuable tool in combatting malicious websites.
And, of course, make sure you're running gateway and desktop antivirus and intrusion prevention products that are up-to-date.
We'll keep you posted as we see more.
Note from the sponsor: eSoft's Gateway AntiVirus and Intrusion Prevention Softpaks provide full protection for this vulnerability and provided that protection starting shortly after the announcement of the vulnerability and well before any exploits became public.