A few years ago, a previous developer added my company's website to a link farm he ran. My company has a wildcard subdomain, so any subdomains will return the user to the homepage. As such, the dev added multiple subdomains to the link farm (e.g., foo.example.com, bar.example.com, foobar.example.com) Before this developer left, he claims to have removed all our links from the link farm. However, to this day, we still get search engines crawling sub-domains that do not exists. I should add that the developer added many, many, subdomain links.
What can I do to prevent these subdomains from getting crawled?