According to Gina Bray, the firm's sales director, the technique only became apparent after Apollo, Vertical Leap's software, highlighted a small drop in a client's search engine rankings.
Further investigation revealed thousands of hidden links at the base of every page of the Web site.
Vertical Leap then found that other sites had also been compromised by the hacker technique.
Although the effects on search engine rankings are minimal, there is a risk that Google could blacklist a site for this kind of hidden linking, even though the site owners have nothing to do with the routing.
The hackers, meanwhile, can drive search engine traffic to almost any site of their choice, including, of course, malware-laden pages.
I suspect that this topic is one we'll hear more about in the months to come. Especially when the technique gets a name...