Data mining involves using sophisticated tools to analyze large datasets and discover patterns. In homeland security, data mining can help identify terrorist activities through records like money transfers and communications. While useful, data mining has limitations - it only finds patterns, not their significance, and does not prove causation. It is also debated if it can reliably predict terrorism given the small number of known incidents. Several US government programs have used data mining for homeland security purposes, but have faced issues around privacy, data quality, and mission creep.