Adobe says:
Critical vulnerabilities have been identified in Photoshop CS2 and CS3 that could allow an attacker who successfully exploits these potential vulnerabilities to take control of the affected system. A malicious BMP, DIB, RLE, or PNG must be opened in Photoshop by the user for an attacker to exploit these potential vulnerabilities. Users are recommended to update their installations with the patches provided below, and Adobe encourages all customers to be cautious before opening any unknown file, regardless of which application they may be using.
Software fixes for both Mac and Windows available from Adobe’s security bulletin, Photoshop CS2 and CS3 updates to address security vulnerabilities.