This is not really SEO related but I found this thread at Google Webmaster Help funny. A parent comes on, asks if there are any other ways porn sites can come up in their Google Web History without having access to their computer.
In short, it appears the parents were away and their son went on their computer. The son then conducted a few adult related searches and clicked on to adult sites. The parent is asking if there is any way that this search history could be easily manipulated. In short, the parent wants to know if their son actually used their computer to look at porn.
The only way, that I know of, to add search history to Google is to conduct searches on Google while signed into that Google account. So if someone hacked into your account and conducted searches, then that might be possible. But typically, hackers won't want to get your son busted for looking for porn. The parent signed off:
This answers my question & I thank you for Google help.
Forum discussion at Google Webmaster Help.