Thirty-two percent of youth in homes with pop-up/spam blockers and 25 percent of youth in homes with filtering, blocking, or monitoring software on their home computers experienced unwanted exposure to sexual material online. This compared with such exposure for 43 percent of households without preventive software installed on the home computer. Among otherwise similar youth, those with pop-up/spam blockers installed on the home computer had 59-percent lower odds of reporting unwanted exposure to sexual material on their home computers; and filtering, blocking, or monitoring software was significantly associated with 65-percent lower odds of such exposure. When data were stratified by youths' gender, the link between preventive software and unwanted exposure to Internet sexual content was similar for boys and girls; however, when data were stratified by age, preventive software was associated with significantly reduced risk of unwanted exposure to online sexual content for 10-12 year-olds and 13-15 year-olds, but not for 16-17 year-olds. The findings suggests that caregivers of boys and girls 15 years old and younger who want to reduce the likelihood of unwanted exposure to sexual material on their home computers should consider using preventive software, particularly filtering, blocking, or monitoring software. Study data were obtained from the Youth Internet Safety Survey-2, a national, random-digit-dialing telephone survey conducted in March-June 2005. The survey involved 800 households (1 caregiver and 1 child between the ages of 10 and 17) with home Internet access. Respondents answered questions that pertained to Internet prevention software on the home computer and adolescents' exposure to online sexual content. 3 tables and 32 references