Hi @pirrone. Thanks for being part of GoDaddy Community! Optin is sometimes related to a subscription form that someone may have on their website. My guess would be that this was a bot that was trying to sign up for a newsletter on your website, especially if you don't already have one. If you can give more details, like the domain for your site and the location of the form, others might be able to provide more suggestions.
JesseW - GoDaddy | Community Manager | 24/7 support available at x.co/247support | Remember to choose a solution and give kudos.