A third of search engine results are poisoned links, says Symantec.

The security vendor uncovered the size of the threat after its researchers spent two weeks investigating the top 100 results when searching for the 300 most popular terms.

In one incident, 99 out of the top 100 search results for a phrase navigated to malicious websites designed to infect web users with malware or steal sensitive personal data such as log-in and passwords.

According to Symantec, search engines such as Google manage to identify and remove only around half of all poisoned links.

Symantec said this makes poisoned search results, one of the most prevalent online threats, along with attacks on social networkers and fake anti-virus.

As a result, the security vendor has made tackling these security issues the focus of its Norton Internet Security 2011 software.

The product, which is currently in beta and can be downloaded for free from Norton's Beta website, comes with Symantec's URL-checking software.

Norton Safe Web Lite checks links displayed in search results from Google, Yahoo and Bing, and alerts the user to any that maybe unsafe to visit.

Symantec confirmed the final version of Norton Safe Web Lite will be made availale later this month.

Noton Internet Security 2011 also features Norton Safe Web for Facebook, which scans Facebook news feeds for malicious URLs, flagging them up before a user clicks through to the linked site.

In the future, Symantec revealed it hopes to extend this tool to other social networks such as Twitter and LinkedIn.

The full version of Norton Internet Security 2011 is expected to be released in September. Pricing details have not yet been made available.

See also: Symantec discovers 44 million stolen gaming credentials