According to a new post on NewScientist.com:
"Web users make a billion visits every month to websites of dubious character, according to a survey enabled by "web crawling" software developed by researchers from Massachusetts Institute of Technology (MIT), US.
The survey, carried out over the last 11 months, found that 5% of all internet traffic was linked to sites that upload unwanted software to a PC, send out spam or attempt to trick users into handing over sensitive information.
The web-crawling software is operated by SiteAdvisor, a company spun-off by computer security researchers from MIT. The company has also launched a web browser add-on that automatically checks the reputation of a site against its database and which can be downloaded as a free trial."
Mobility has always been a risky business....