## 1 Introduction  
The growing use of social networks has provided a channel to unrestrictedly express feelings and opinions on a mass scale. However, one of the negative aspects is that this has caused an increase in harassment, the so-called cyberbullying, defined as the use of information and communication technologies, like e-mails, text messages from cell phones, social networks, to support the deliberate, repeated, and hostile behavior of an individual or group to harm others, through personal attacks, disclosure of confidential or fake information, among other aspects [1]. According to [2], between 2005 and 2018, there was an increase in cyberbullying cases in Latin America. This study detected the existence of a high percentage of related situations: between 3.5% and 58% of cyber-victims; and between 2.5% and 32% of cyber-aggressors. Those involved are mainly men. In the particular case of Chile, according to [3] study led by PUCV with financing from MINEDUC, and under the agreement with UNESCO-Santiago, 20% of those surveyed, reported having been treated offensively or in an unfriendly manner by other people. These experiences are 58% in-person cases (without excluding other forms), 28% through a social network, 25% by messaging, and 13% through an online game. A total of 14% of children who use the internet acknowledge having treated another person offensively or rudely in the last year. 76% of these interactions have been face-to-face, 19% through social media, 18% by messaging, and 11% through cell phone messages. Generally, bullying and cyberbullying begin in primary school. This continues in high school, where it reaches its peak. In some cases, these behaviors continue after high school, leading to social isolation, truancy, and low grades [4; 5]. Generally, cyberbullying starts with aggressive and repetitive messages from one person or a group of people to another person, where an aggressor and a victim can be seen. Table 1 shows some of the types of cyberbullying [6]. These types of cyberbullying share common elements, like the intention to cause harm and the sending of messages with aggressive and offensive content. Hence, it is important to create detection mechanisms of aggressive messages as a first step for the early detection of cyberbullying. Natural Language Processing (NLP) can provide important mechanisms to detect aggression in texts. NLP is an area of research and application that explores how computers can be used to understand and manipulate human expressions in text [7]. NLP addresses different areas, like computing and computer science, linguistics, math, artificial intelligence, and psychology, among others. In recent years, the use of different techniques has been popular to identify the emotions that the author of a comment or message wishes to transmit. Text subjectivity analysis is found as an NLP subcategory. This oversees extracting and classifying the different emotions that the author of a text wants to transmit, and with this obtain valuable information to analyze its content. The analysis of text subjectivity provides different tools that allow detecting aggression in text written on social media. There is consensus in the benefits that the early detection of aggression in messages sent by users provides, allowing taking preventive measures, and thus avoiding the consequences of cyberbullying. Given that most aggression detection works in texts prior to 2018 have been made for the English language, it seems to be important to focus this work on the analysis of aggression in texts written in the Spanish language. Using the previous work of the Universidad del Bio-Bio research group SoMos, the use of a hybrid approach based on