Google's advert platform is much more likely to show highly paid executive job vacancies to men than women, researchers have discovered.

It is common knowledge that technology companies track our internet usage and display adverts based on what we look at and who they think we are, but little is known about how the complex algorithms actually work.

Tackling this, researchers from Carnegie Mellon University and the International Computer Science Institute created a tool called AdFisher to get a better understanding of how targeted advertising works. AdFish found that of two identical job seekers, the man was more likely to be offered high-paid jobs than the woman when they visited a news website.

Google users can tell the search engine more about themselves, such as their age (if it has guessed incorrectly), language spoken and interests through the Google transparency tool. But where browsing to certain websites will return predictable results, a user's behaviour does not always result in a change to Google's profile of you on the transparency page.

AdFisher works by acting as thousands of web users, each taking a carefully chosen route across the internet in such a way that an ad-targeting network like Google Ads will infer certain interests and characteristics from them. The programme then records which adverts are displayed when it later visits a news website that uses Google's ad network. It can be set to act as a man or woman, then flag any differences in the adverts it is shown.

Anupam Datta, an associate professor at Carnegie Mellon University, said in the MIT Technology Review: "I think our findings suggest that there are parts of the ad ecosystem where kinds of discrimination are beginning to emerge and there is a lack of transparency. This is concerning from a societal standpoint."

Datta and his team are currently building a version of AdFisher to analyse how Microsoft's Bing search engine serves up adverts to its users.

Google says it is looking into the methodology of Datta's study to try and understand its findings. A spokeswoman for the search giant told MIT: "Advertisers can choose to target the audience they want to reach, and we have policies that guide the type of interest-based ads that are allowed. We provide transparency to users with 'Why This Ad' notices and Ad Settings, as well as the ability to opt out of interest-based ads."