http://www.domaintools.com/about/terms-of-service/:
Memberships and Services are offered at our sole discretion and may be temporarily or permanently disabled at any time for any reason, including but not limited to the use of fraudulent, stolen or incorrect payment credentials or instruments on the Site, the failure to respond to a request for verification of payment credentials, or the use of automated processes or scripts to access or obtain information from DomainTools .