NOTE: This post has been updated to include clarifications that were made to the original study.

A study released Tuesday shows that 45% of the top 185 U.S. websites transmit identifying details about their visitors to at least four outside websites.

The data transmitted was primarily a "username" – which is the name a person uses to log into a website – or a user ID assigned by the website to a user. It was usually transmitted through referrers – which is information about the web page transmitted automatically.

In some cases, the data went much further: the study found for instance that the online dating website OKCupid sent the gender, age, zip codeto two companies that sell personal data in auctions, BlueKai and Lotame. Lotame also received data about 'relationship status' and 'drug use frequency.'

Lotame confirmed that it has a data licensing relationship with OKCupid, but said it does not use data in the "drug use category." "We do capture standard demographic attributes like zip, age and gender from several publishers," a BlueKai spokesperson said.