单词poison-pen letter
n.: 恶意的匿名信；匿名诽谤信网络: 黑信
恶意的匿名信；匿名诽谤信:
an unpleasant letter that is not signed and is intended to upset the person who receives it
Someone gave my boss a poison-pen letter.
有人写了一封黑函给我的老板。