Over on The Drip, Lucy Mazalon just published a pretty good article on how to help eliminate spam leads from Pardot. Spam leads or fake leads, garbage entered into signup forms, don't do anybody any good. At best they waste the system's time and inflate your sending numbers with subscribers who are never going to engage. At worst, they could be spam traps that sending mail to will end up harming your sending reputation. I generally agree with the guidance given here -- especially the recommendation to enable reCAPTCHA to make it harder for bots to submit garbage.
Keep in mind, though, that even with reCAPTCHA, a determined bad guy could put drop garbage in manually. The way to prevent this is with confirmed opt-in or double opt-in. If you're worried about garbage entering your subscriber stream, or you're having trouble with low engagement rates or spamtrap-driven deliverability issues, you really ought to consider this. How to implement COI/DOI with Pardot can be found here.
If you're curious about how double opt-in works and want to try it for yourself, you can click here to sign up for Spam Resource emails or click here to sign up for my song-a-day email. My personal list manager tool uses double opt-in to confirm consent, keep garbage out, and verify your email address.
Do you subscribe to The Drip newsletter? If you're a Salesforce Pardot user, I recommend signing up. I'm so deliverability-focused that of course not all its content is meant for me -- but that's OK! If you're more of a generalist or marketing strategist, I think you'll find their content compelling. Click here for more information or to sign up.