Apple released iLife Support 8.3.1, a security-related update for the companyis iLife suite, as well as for Aperture 2. The update patches two issues that deal with maliciously crafted TIFF images, both of which could allow the bad guys who made that image to take over your Mac. The patch also addresses a similar issue regarding maliciously crafted JPEGs.
The update is an 11.7MB download. Currently, weire only seeing it at Appleis support site, but it is likely to show up in Software Update shortly. You can find more detailed information in a Knowledge Base article Apple has published for the update.