they are only finding how many bugs in their system. not for hacks their users e-mails. Yahoo is So Big Company and they will no do this kind of stupid things. So not to Scared. Be yahoo.
same sought of work was done by relience in past they gonna hire all hackers and in result they wil be saved from hacking hehehehe
Oh you can bet the hackers had to sign non-disclosure agreements, regardless of whether they were looking at code for unreleased projects or the whole system or whatever.