Due to a recent dramatic increase in sign ups from bots, we've had to introduce the use of a Captcha on all sign ups of personal accounts. We're using the well known reCAPTCHA service, which not only helps prevent fraud, but also helps in the digitisation of historic books and texts. reCAPTCHA also has an audio challenge for vision impaired people, making it high accessible for all users.
For Guest accounts, we still require a backup email address, and for all paid accounts, we still highly recommend a backup email address. We'll never send spam to your backup address, and will only use it to send important messages, like if you request your lost password, or you're approaching your email usage quota.