Microsoft has attracted criticism for using in-line embedded text ads to promote its own search engine along with its search marketing customers' messages.
The Redmond giant's adCenter programme began using the IntelliTXT method, which makes textual content into sponsored links, to attract traffic. But some adCenter clients whose ads are displayed at destination pages on Live Search have complained.
The move came after changes were made to the adCenter terms and conditions, so that Microsoft "may use matching criteria other than keyword searches to display your advertisements".
But a disgruntled adCenter client discovered that one of the techniques involved using in-line sponsored links on content sites to send web users to Live Search results pages bearing clients' paid search marketing adverts.
"I hovered over one and saw it was for Live Search", wrote search marketing director Melissa Mackey. "When I clicked on it, I was taken to a Live Search page for one of our PPC keywords, with our ad on it. All of a sudden, our ROI on that keyword plummeted as a result.
"I wondered why we had a pocket of keywords with huge leaps in clicks and no resultant increases in conversions. This sucks. Is MSN really so desperate for traffic that they've resorted to running crappy ads for their own search results?"
Separately, Mackey complained that, while clicks on her sponsored keyword doubled, conversions remained static, halving the effectiveness of her campaign.
A Microsoft adCenter spokesperson confirmed the practice, saying:
"The examples were part of a marketing campaign to drive trial and interest in Live Search itself".
According to the spokesperson, search marketing clients will be able to opt out of having their ads placed in content. But the episode has provided impetus for a rash of criticisms aimed at adCenter.
In March, Microsoft enjoyed only a 10.1% share of the search market, according to Nielsen//NetRatings - behind leader Google and second-placed Yahoo!.