 In August 2015, Dropbox announced the availability of "Universal 2nd Factor" USB security keys, providing two-factor authentication for logging into its services.Dropbox received initial funding from seed accelerator Y Combinator.Dropbox also raised US$1.2 million in Series A funding from Sequoia Capital in 2007, that "along with interest (on that amount) converted to equity as part of the Series A investment, which included a fresh slug of US$6 million", bringing the total amount to US$7.25 million, with the round closed in 2008 and documents filed in 2009.