A method for detecting a SQL injection attack comprises a training phase and a detection phase. In the training phase, a plurality of SQL queries is transformed into a respective plurality of SQL token domain queries which are processed using a n-gram analysis to provide a threshold and an averaging vector. In the detection phase, each newly arrived SQL query is transformed into a new SQL token domain query, and the n-gram analysis is applied together with the averaging vector and the threshold to each new SQL token domain query to determine if the new SQL query is normal or abnormal. The detection may be online or offline.