Recently, the Advanced Threat Response Team of 360 Core Security Division detected an APT attack exploiting a 0-day vulnerability and captured the world’s first Office malicious sample that uses a browser 0-day vulnerability. We code named the vulnerability as "double kill” exploit. This vulnerability affects the latest version of Internet Explorer and applications that use the IE kernel. When users browse the web or open Office documents, they are likely to be potential targets. Eventually the hackers will implant backdoor Trojan to completely control the computer. In response, we shared with Microsoft the relevant details of the 0day vulnerability in a timely manner. This APT attack was analyzed and attributed upon the detection and we now confirmed its association with the APT-C-06 Group. On April 18, 2018, as soon as 360 Core Security detected the malicious activity, we contacted Microsoft without any delay and submitted relevant details to Microsoft. Microsoft confirmed this vulnerability on the morning of April 20th and released an official security patch on May 8th. Microsoft has fixed the vulnerability and named it CVE-2018-8174. After the vulnerability was properly resolved, we published this report on May 9th, along with further technical disclosure of the attack and the 0day.