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1. Creating a data set

The first stage was the creation of two lists of telephone numbers. The second stage consisted of searching for data sources that were spread by the telecom over eight separate key databases [2].

2. Categories of subscribers:

The following three categories of subscribers were defined:

• Subscription fraudulent: Most consumers in this group do not pay their bills at all. Because of unusual activity in long distance calls within 6 months after the implementation date, the line is usually blocked [2].

• Insolvent: There are two or more unpaid bills for subscribers with a maximum debt of less than 10 times their monthly payments [2].
• Normal: Customers with their bills up to date [2].

3. System architecture: The proposed subscription fraud prevention system consists of two modules: a classification module and a prediction module [2].