If you allow your children or students to use the Internet while unattended, then you probably want to consider a filtering tool like Net Nanny. This parental control service ($40/year) does an excellent job of filtering Web content, setting Internet access times, and even managing PC game use.
This service appears to be more sophisticated than other parental control offerings I've tried. Like the competition, Net Nanny lets you set up user accounts to customize--but in addition to selecting content categories to block, you can also control access to specific URLs, block inappropriate Web searches, and even limit Internet access to specific sites. It also monitors browsing, chat, IM, and social networking usage and provides usage reports. Also great: You can set Override passwords so that adults can view content that's off limits to children.
Net Nanny worked well in my testing. It installed smoothly, was easy to use, and did its work quickly. I experimented with setting filters in one browser window while viewing the results immediately in another window. Net Nanny uses the Safe Search features found in most popular browsers to filter objectionable content from search results. For example, when testing a competing product, I searched on "Spring Break" and received the expected page full of thumbnail images showing scantily clad young women and men drinking heavily, with links to student blogs. The same Google search using Net Nanny yielded a list of articles on the history of spring break, along with perfectly appropriate beach photos.
Net Nanny is an invaluable tool for parents and teachers who want to control how children and teens access the Web.
Note: This download runs a lightweight installer that asks for your e-mail address to set up a trial account, then provides a registration code. I have not had problems with spam to the address that I provided during testing.