Both updates are available through only the Software Update system in OS X.
Patching a security weakness identified earlier this month, Apple's Security Update 1.0 prevents unauthorized access to root in OS X. Without the update, applications opened from the Recent Items folder could give root access without requesting an administrator's password.
Microsoft has released its own Internet Explorer Security Update. This stops Internet Explorer 5.1 (which runs only in Mac OS X) from launching and running downloaded files automatically.