The number of New York-based apartments listed on Airbnb in 2014 that would be illegal rentals grew by 2,300 from the previous year, representing 60% of the total number of units in the five boroughs listed on the site, according to data compiled by Tom Slee, a writer who runs a data technology site. Mr. Slee's data was provided by Share Better, an anti-Airbnb lobbying group, although a spokesman said Mr. Slee was not paid for his work.
The analysis flagged Airbnb listings that showed an entire apartment available. Rooms, not whole apartments, can be rented out under New York state law, as long as the apartment is occupied during the guest's stay.
The number of units being rented by people listing two or more apartments grew by 700 units, according to Mr. Slee's data. Approximately 30% of Airbnb’s inventory in New York City is listed by users who are illegally renting out multiple residential units, including 207 users renting out five or more units.