Evolutionary computation is used to construct undetectable computer attack scripts. Using a simulated operating system, we show that scripts can be evolved to cover their tracks and become difficult to detect from log file analysis. Categories and Subject Descriptors I.2.6 [Learning], I.2.8 [Problem Solving, Control Methods, and Search] General Terms Algorithms, Economics. Keywords Hacker, script kiddies, agent-based model, log analysis, vulnerability assessment.