Used by User Interface designers and abused by online advertisers, pop-up windows are one of the most prevalent modalities in computing environments. Most often associated with delivering advertising content (which made them infamous) online, pop-up windows are also common offline where they deliver warnings, alerts, or other system information to computer users. Yet, little is known about how pop-ups affect the processing of information in and around themselves. The present study proposes that three different mechanisms, derived from attentional spotlight, limited capacity, and affect-as-information models, could explain the effects of pop-up presence on the extent and nature of information processing on a Web page. A 2 (same vs. different pop-up location) x 2 (number of pop-ups—one versus three) x 2 (pop-up content—advertisements vs. factoids) factorial experiment was employed to test the above-mentioned mechanisms. Free recall and recognition of the various news stories on the Web pages where pop-ups appeared were used to indicate the extent and nature of information processing. At the same time, facial EMG, skin conductance responses and heart-rate measures were measured in order to assess the attention-getting, interruptive, and annoying nature of pop-up windows that are implied in the three mechanisms. The findings suggest that pop-ups direct users‘ attention towards a specific location on the screen, and that information located in their vicinity benefits from this movement of the attentional spotlight. Theoretical and practical implications are discussed.