Goatse Security exploited a security hole in AT&T’s 3G service on iPad. Goatse exploited a feature that pre-populates your email address using the ICC-ID, so you don’t have to type the email address every single time. The breach appears to be limited to iPad 3G users’ ICC-IDs and email addresses associated with them. How many accounts were exposed is still an open question, since AT&C is “doing the forensics as we speak” and until they’re completed, there’s “no way of validating” the number of addresses.”]
Source: https://gizmodo.com/the-little-feature-that-led-to-at-ts-ipad-security-brea-5559686