New York: Smartphone users in the US are getting increasingly concerned about having their activity tracked to serve them targeted ads, a study has found.

The online study conducted by global market research firm Ipsos on behalf of TRUSTe - a leading global Data Privacy Management (DPM) company - suggests that most smartphone users are uncomfortable with the idea of online behavioural advertising (OBA).

"Our research shows that the majority of Americans (68 percent) are still uneasy about having their online activity tracked for use in targeted ads, mainly because they feel like they have limited control," said Chris Babel, CEO of TRUSTe.

However, research also showed that awareness of the "AdChoices" icon, part of the Digital Advertising Alliance (DAA) Self-Regulatory Programme for OBA, jumped to 37 percent.

This programme provides users with more control over their online ad experience with the option to opt-out of personal targeting.

"As more and more consumers understand how their information is being tracked and the choices they have to opt-out, the more we'll start to see consumers embrace the concept of Online Behavioural Advertising and realise the benefits, such as receiving great deals from their favourite online retailers," Babel said in a press release.

One in three (33 percent) said that the information available on AdChoices, along with the option of opting out of OBA would make them feel more positive about the concept of targeted ads.

According to the survey, lack of consumer trust is currently affecting how consumers are using the internet as 77 percent of US consumers who say they worry about their privacy online moderated their online activity in the previous 12 months due to privacy concerns.

The research was done using an online survey among a representative quota sample of 1,000 adults aged 18-75 in the US.

Among these, 537 were smartphone users and 978 said they worry about their privacy online.