The anonymous hacker group publicized username and phone number information as a means of exploiting Snapchat's lackadaisical approach to patching a security bug that would've prevented this. SnapchatDB (since suspended) publicized a database covering 76 of the United States' 322 area codes. Luckily (if it's possible to find a silver lining), the last two digits of each leaked phone number were censored to "prevent abuse." The people behind the database would, however, release the uncensored information under the right circumstances if contacted — something they encouraged the public do.
While all those ephemeral photos users casually send across space weren't at risk (you can still make that funky duck face for your close friends without worry), the public information has the potential to lead to other social media profiles. Since most people use the same username across the web, and with the bonus phone information, unearthing a Facebook or Twitter account is that much easier. A hacker could then find e-mail addresses, which could lead to credit information, and suddenly the rabbit hole is deeper than previously thought. Though less than a quarter of the nation's area codes were affected, 4.6 million people is no joke. You can find out if your account was hacked by going to this site. (Valley Wag)