Google could be earning close to half a billion dollars annually from advertisements placed on typo domains, according to a new study. For example, should a user accidentally enter an incorrect website address like twittter.com, he may be led to an alternative website owned by a cybersquatter. And if he clicks on a Google Adsense ad, the publisher makes money, and so does Google.

Although Harvard University researchers Tyler Moore and Benjamin Edelman claim that “it is difficult to know exactly how many people visit typosquatting domains“, but that doesn’t hinder them from figuring out the estimated number of visitors reaching typo sites, as well as the fees advertisers pay to Google.

In a study released in January, the pair estimates that at least 938 000 typosquatting domains target the top 3,264 .com sites, hoping that a user would misspell the URL. Crawling more than 285,000 typo domains to analyze their revenue sources, the study revealed that around 80 per cent were supported by pay-per-click ads, spiraled by Google’s “Adsense for Domains” program. Gathering data from Amazon’s web ranking company Alexa and common spelling mistakes using the Damerau-Levenshtein distance, Moore and Edelman generate a list of popular domains that could tempt a squatter to register many typo domains. For example, faceboolk, facebok, faceboik, and faceboko each have a Damerau-Levenshtein distance of 1 from facebook.

They also found out that visitors to a site’s typo domains total 0.7 per cent of visits to the genuine site. Extrapolating this percentage to the top 100,000 most popular sites on Alexa, they estimate that typo domains collectively receive a massive 68.2 million daily visitors. “If these typo domains were treated as a single website, that site would be ranked by Alexa as the 10th most popular website in the world,” they write, “It would be more popular, in unique daily visitors, than Twitter.com, Myspace.com, or Amazon.com.”

Despite Google keeping mum about the revenues earned from the “Adsense for Domains” program, Moore and Edelman managed to pull data from other sources, which claimed that Google makes 3.5 cents per visit to typo domains. Taking into account these factors, the researchers concluded that URLs typos net Google a tidy sum of $497 million revenue per year. This figure translates to 7 per cent out of $7.16 billion earned from Google Adsense in 2009.