https://www.facebook.com/whitehat
Exclusions
The following bugs are not eligible for a bounty (and we do not recommend testing for these):
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Denial of Service Vulnerabilities
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That said, they do appear to be quite hypocritical when it comes to enforcing this, as at least one user on the /r/netsec thread claimed that Facebook paid them for a mail bombing vulnerability.I guess you have to use this to attack high-profile targets (or Facebook themselves) until they notice.