Great strides have been made in recent years in boosting public trust in the online advertising industry.
But Robert Madelin, a former Director General in the European Commission, cautioned that more still needs to be done.
He said, "When it comes to trust, some companies and sectors are still in the 19th century and just don't get it. Trust in online advertising is a huge thing but it has to be earned."
Madelin, senior innovation advisor at the European Political Strategy Centre, was a keynote speaker on Tuesday at the first-ever summit organised by the European Interactive Digital Advertising Alliance (EDAA).
The EDAA was founded by a European industry coalition representing advertisers, the advertising agency sector, direct marketing and the media.
Its principal purpose is to deliver and maintain a self-regulatory programme for the Online behavioural advertising (OBA) industry and to certify the 'OBA icon' to companies involved in online advertising.
Also known as interests based advertising, OBA tracks a user's online activity, such as websites viewed, then delivers advertising or marketing content that matches that activity.
The OBA icon is an interactive symbol that also links consumers to an online portal (http://www.youronlinechoices.eu/) where they can find easy-to-understand information on OBA.
Madelin's comments at the opening session of the day-long summit, which was attended by 150 people, were echoed by Townsend Feehan, CEO of the European-level association for the interactive advertising industry, IAB Europe.
Both trust and "responsible" advertising were, she noted, "existential" necessities for the online advertising sector.
Feehan heralded the impact of the self-regulatory OBA programme, pointing out that it had been adopted across 33 countries since it was launched.
Further comment came from Jon Chase, director of Velvet Rock Communications, who said, "It's become increasingly important for advertisers to be seen to advertise responsibly, especially in the online sector."
"Communicating to the public what we are doing is also crucial. This can help knock down some of the trust barriers."
Addressing the thorny issue of what can be done to "stem the tide" of advertising bloggers, Dominic Lyle, DG of the European Association of Communications Agencies, said, "Clearly, we have got to find cleverer ways of getting our brand messaging across, particularly in the mobile space."