"On the web the thinking of cults can spread very rapidly and suddenly a cult which was 12 people who had some deep personal issues suddenly find a formula which is very believable," he said. "A sort of conspiracy theory of sorts and which you can imagine spreading to thousands of people and being deeply damaging."
Sir Tim and colleagues at the World Wide Web consortium had looked at simple ways of branding websites - but concluded that a whole variety of different mechanisms was needed.
Sir Tim spoke to the BBC to publicise the launch of his World Wide Web Foundation which aims to improve the web's accessibility.
Alongside this role it will aim to make it easier for people to get online. Currently only 20% of the world's population have access to the web