Four out of 100 US search engine results link to risky Websites, according to McAfee's "The State of Search Engine Safety" report.
The report rated search results as unsafe if the Websites to which they linked distributed adware, sent a lot of spam or made unauthorized changes to a user's computer.
High volumes of "non-spammy" e-mail, pop-up ads and prompts for users to change browser settings were also flagged as risky.
The percentage of unsafe search results dropped since May 2006, when 5% were deemed dangerous, thanks mainly to safer sponsored results. Sponsored results still contained 2.4 times as many risky sites as organic results.
The report stated that dangerous sites were present in search results for all five of the top US search engines, representing 93% of all search engine use.
Some 80% of Website visits originate from search queries.