One father says he makes sure he can see from his home office what his children are doing on the Internet, and a police officer advises that parents have to have parental control or filter software on their computers. Office Steve DeWarns of California has said parents have to set limits based on age and maturity in the physical world, and the same should be done in cyberspace. The problem is exacerbated when parents feel intimidated by technology and lack understanding of how to install software that filters out porn sites. Parents also have to overcome their unwillingness to limit their children's horizons or snoop through their messages to monitor their activities on social networking sites. In conducting oversight, says Neil Rubenking, who is a software analyst, his preferences are traditional parenting techniques, including providing explanations to children as to why they should avoid unsavory Web sites and other possible dangers. The reason is that children soon find out that they can get around filtering software, possibly at the home of a friend. Blocking programs have been improving, says Mr. Rubenking, and he points out that many parents would rather not spy on their children. However, say safety experts, the fact that sexual predators can use the Internet to scan for victims without being noticed in many cases means that parents simply cannot let down their guard.