This study aims to investigate the initial perceived knowledge and skills of high school students in information technology (IT) security and the effect of an online security support tool, the Security Portal (SP), on students’ perceived knowledge and skills in IT security. The SP is a website designed and developed as an extracurricular learning tool to improve high school students’ knowledge and skills in IT security. An exploratory research design with descriptive and inferential statistical analysis was conducted to answer the research questions. The data were collected from the participants through the Perceived Knowledge and Skills in IT Security questionnaire, administered as pre-test and post-test before and after using the SP. The results of the study indicated that the majority of students were not aware about their schools’ IT security policies and rules. Similarly, students had limited knowledge of the rules for using IT devices at their homes. Students’ perceived knowledge and skills in (i) virus infection, (ii) awareness about IT crimes and unlicensed products, (iii) security settings of operating systems, (iv) Windows firewall and defender, (v) security settings of Android OS except adding owner information (vi) security issues related to e-mails, except risk associated with opening e-mails from unknown senders, (vii) security issues of web browsers and SNSs except security and privacy settings of SNSs, could be improved by using such tools.