Our website has an email signup form, as did our Facebook page. A few months ago we began getting anywhere from 10-40 fake signups a day. We deleted the Facebook form and instituted a reCAPTCHA on the website form, but are still getting a large number of SPAM signups. I can't figure out where they're coming from or how to stop them.
I'm sorry to hear you're receiving a lot of bad contact sign-ups. I would recommend contacting our Account Review team for additional resources that might benefit you. Generally, the captcha is the best line of defense with spam sign-ups, but the Account Review department is the best qualified to review the current standards of your contact import process and offer more assistance. They can be reached at 866.433.8499 (U.S.) or 339.222.5900 (International) and are available 8AM to 10PM ET Monday through Thursday and 8AM to 9PM ET on Fridays.