- Six vulnerabilities in an open-source image format could allow intruders to compromise computers running Linux and may allow attacks against Windows PCs as well as Macs running OS X. The security issues appear in a library supporting the portable network graphics (PNG) format, used widely by programs such as the Mozilla and Opera browsers and various e-mail clients. The most critical issue, a memory problem known as a buffer overflow, could allow specially created PNG graphics to execute a malicious program when the application loads the image.