DETERMINING THE SAMPLE LENGTH OF THE ELECTRONIC LETTERS MODEL
In the conditions of intensive development of various spheres of activity of the state and society, the use of advanced information technologies becomes one of the most important and often decisive factors that determine the effectiveness of all levels of management. Information technologies hold a strong position in everyday life and in various spheres of government activity. Information systems of various types and purposes are being introduced for processing and analyzing information, forecasting and supporting management decisions making at various levels. The functioning of almost any organization in a varying degree depends on how efficiently and steadily its information system works, how reliably its information resources are protected from various information security threats, one of which is spam. It is worth noting that there have been many attempts to solve the problem of its detection once and for all. Research is ongoing in this subject area constantly. Based on its results, various approaches are proposed and implemented in practice. They are mostly based on the well-proven basic statistical processing of various parameters of emails. At the same time, the content of e-mails is not fully taken into account, which leads to an increase in the number of Type I errors. To address this issue, the authors previously proposed a model of emails that takes into account the content of emails, which often changes depending on the tasks performed by users and their changing information needs. Its key feature is that it operates with data obtained from the original text of emails and converted into a numeric vector. As the parameters of the model of emails that influence the selection of emails test segments, which are a reflection of their distinctive features, the authors identified: the number of numeric codes associated with text characters in the function of converting letters to numeric vector; the step of fetching text characters in the function of converting letters to a numeric vector; sample length (length of the «generator» - the sequence that generates the «gene»). Purpose of the research: to assess the influence of the sample length (length of the «generator» - the sequence that generates the «gene»), which is the email model key parameter, on results of the use of the model in spam detection. Methods: use of decision rules of the implicative type «IF ..., THEN ...». Results: the results of the experiment confirm the correctness and applicability of the email model previously developed by the authors. At the same time, the application of the e-mail model gives the best detection results when the numerical value of the sample length (the length of the «generator» - the sequence generating the «gene») is equal to 1 or 2, which is confirmed by the values of the aggregated assessment measure (the value combining the measures of completeness and accuracy of detection and representing their harmonic mean). When the length of the «generator» is greater than or equal to 3, the detection results deteriorate on average by more than 10 %. The inexpediency of using the «generator» length values greater than or equal to 3 is justified by an unacceptable decrease in the values of the detection completeness and the aggregated assessment measure. Practical relevance: the authors' model of emails and an approach to spam detection allow to highlight the sequences of text characters corresponding to the characteristics of a certain class of emails, and to make the spam detection process individual for the recipient.