Apple has issued a security update for Mac OS X, which fixes various vulnerabilities.
1) Multiple vulnerabilities in libpng can be exploited by malicious people to cause a DoS (Denial of Service) or compromise a user's system.

For more information:

2) A vulnerability in the Safari browser can be used by a malicious website to steal sensitive information from forms.

The vulnerability can reportedly only be exploited in the situation of a form being sent with the POST method to an URL, which performs a redirection to another URL.

3) A vulnerability in the processing of network traffic can be exploited by malicious people to cause a DoS.

The vulnerability is exploited by sending a sequence of specially crafted IP fragments. The attack known as the "Rose Attack" will cause the system to use too much system resources resulting in DoS.

Apply Security Update 2004-08-09.

Mac OS X 10.3.5:

Mac OS X 10.2.8:

Other References: