Sir Tim Berners-Lee, the inventor of the worldwide web, has warned that the widespread collection of personal data and the use of poorly understood algorithms on the internet are leading to the spread of misinformation and targeted political campaigns.

Writing in an open letter marking the 28th anniversary of his invention, he said many people obtained news and information from a few social media sites and search engines. Companies like Facebook and Google make money through clicks they show users based on personal data and online behavior.

"They choose what to show us based on algorithms which learn from our personal data that they are constantly harvesting," the British computer scientist wrote. "The net result is that these sites show us content they think we'll click on – meaning that misinformation, or 'fake news', which is surprising, shocking, or designed to appeal to our biases can spread like wildfire," he warned.

Berners-Lee said the solution is not to create central bodies to determine what is true or not, but rather gatekeepers like Google and Facebook should continue to combat the problem of spreading misinformation. At the same time, he advocated for more transparency in how algorithms are used.

Many companies provide free online services in exchange for personal data, but "we're missing a trick," because the data is held in "proprietary silos" that users have no control on how or with whom it is shared, Berners-Lee said.

'Chilling effect' on free speech

The widespread data collection has the side effect of infringing on privacy rights. "Through collaboration with - or coercion of - companies, governments are also increasingly watching our every move online, and passing extreme laws that trample on our rights to privacy," the founder of the Web Foundation said.

The dangers to political opponents or writers living under repressive regimes is clear, but even in democracies "watching everyone, all the time is simply going too far," he wrote.

"It creates a chilling effect on free speech and stops the web from being used as a space to explore important topics, like sensitive health issues, sexuality or religion," he wrote.

Another trend that emerged during the 2016 US election was the use of sophisticated online political advertising. As most people get information from a limited number of platforms that use complex algorithms taken from personal information, political campaigns are able to directly target users with messaging.

"There are suggestions that some political adverts - in the US and around the world - are being used in unethical ways - to point voters to fake news sites," he said. "Targeted advertising allows a campaign to say completely different, possibly conflicting things to different groups," he wrote, questing whether or not that practice was democratic.