The greatest threat to our modern information infrastructure is the remote exploitation of program vulnerabilities—31 out of 34 CERT advisories year-to-date are due to such exploitations. Saman Amarasinghe explains many ways in which malicious code, typically inserted into a computer system masquerading as data, can allow unauthorized access to a vulnerable privileged program. Buffer overflow, format string vulnerabilities and execution models for legitimate programs will be discussed. From the Series:CSE Colloquia - 2003