Mike Harris of Illinois and Jeff Dunstan of California accuse the firm of “secretly” bundling its tracking software with various other programmes, such as free screen savers or games. They allege that “in many cases, the existence of the surveillance software… is only disclosed, in an inconspicuous fashion, after the installation process has already begun”.

Harris and Dunstan allege that ComScore’s software collects a computer user’s usernames and passwords, their search engine queries, what websites they visit, the ads they click on, the goods they purchase and credit card numbers.

ComScore says that after an initial review of the claims it believes “they are without merit”. The company intends to “vigorously protect and defend itself,” according to a statement.