Websites opposing vaccination are prevalent on the Internet. Web 2.0, defined by interaction and user-generated content, has become ubiquitous. Furthermore, a new postmodern paradigm of healthcare has emerged, where power has shifted from doctors to patients, the legitimacy of science is questioned, and expertise is redefined. Together this has created an environment where anti-vaccine activists are able to effectively spread their messages. Evidence shows that individuals turn to the Internet for vaccination advice, and suggests such sources can impact vaccination decisions - therefore it is likely that anti-vaccine websites can influence whether people vaccinate themselves or their children. This overview examines the types of rhetoric individuals may encounter online in order to better understand why the anti-vaccination movement can be convincing, despite lacking scientific support for their claims. Tactics and tropes commonly used to argue against vaccination are described. This includes actions such as skewing science, shifting hypotheses, censoring dissent, and attacking critics; also discussed are frequently made claims such as not being "anti-vaccine" but "pro-safe vaccines", that vaccines are toxic or unnatural, and more. Recognizing disingenuous claims made by the anti-vaccination movement is essential in order to critically evaluate the information and misinformation encountered online. Copyright © 2011 Elsevier Ltd. All rights reserved.