Following accusations of bias, several internet search engines claim to have taken steps to clearly mark listings to help users discern between web content and advertisements.

Fred Bullock, AltaVista's chief marketing officer, explained that the paid listings displayed on its website are delineated from its search results and are not misleading.

AltaVista, a unit of CMGI, is one of several search services that uses advertisements, or paid listings.

AOL said that it separates a list of 'sponsored links' at the top of its search page before listing other search results.

Earlier this year, Terra Lycos said that it had begun to label its paid results 'sponsored searches' instead of 'from our partners' to clarify that they are ads.

LookSmart and IWon simply label the paid results 'featured listings' without providing any further explanation.

The changes have been brought about by Federal Trade Commission warnings to seven internet search engines that they should fully disclose that paid advertisements are included in their search engine results.

The warnings, which included a list of labels which the Commission believes are inadequate, such as 'featured listings', 'recommended sites' and 'search partners', were sent to AltaVista, AOL, IWon, LookSmart, Microsoft and Terra Lycos.

An earlier study by the Consumers Union discovered that 60 per cent of the public were unaware that a number of commonly used search engines are paid to list some sites more prominently than others.

Meanwhile, AltaVista has unveiled Prisma, a new technology that it claims will give more rounded search results.