Eight out of 10 people said they would not disclose their incomes online and yet nine out of 10 of the same group did just that, according to research conducted by AOL.
The study, which covered a sample of 1,000 web users, found that while 84% of consumers said they would not give away details of their incomes, 89% willingly did, without pressure or persuasion.
The research also revealed that 34% of consumers expect to become the victims of online credit card fraud, but only 11% have actually experienced it.
Jules Polonetsky, AOL's chief privacy officer, said: "Our research identified a significant gap between what people say and what they do when it comes to protecting sensitive information online."
The research's publication comes as AOL launches a privacy education campaign, which features an animated penguin that explains to web users how behaviourally targeted advertising works as they surf the internet.
Polonetsky said: "Personalising content and delivering relevant advertising online will only succeed for consumers and for advertisers if it is done in a trustworthy and transparent manner.
"In addition, business and government will need to offer approaches that recognise that at certain times personalisation and data use will be welcomed, and in other cases, users will demand limits on the use of their data."
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