The purpose of the study was to contribute to the overall understanding of terrorist organizations’ use of the Internet and to increase researchers’ knowledge of Web site effectiveness. The methodological approach was the evaluation of the perceived credibility of Web sites based on existing criteria derived from information users. The Web sites of four terrorist organizations were assessed: two secular nationalist groups, the People’s Front for the Liberation of Palestine (PFLP) and Liberation Tigers of Tamil Elam (LTTE or Tamil Tigers); and two religious nationalist groups, Hamas and Hezbollah. The findings of this analysis showed differences in perceived credibility factors among terrorist organizations’ Web sites and positive levels of perceived credibility for the Web sites. These findings indicate the potential for positive impressions of the organizations’ Web sites by information users, which would help empower the organizations with the capacity to reach their objectives. By using Web sites, these groups can effectively increase their support base through disseminating information, improving recruiting, and attracting monetary contributions, and can establish themselves as legitimate components of society.