Google is accusing North Korean hackers of sending malicious files to cybersecurity researchers in a months-long attack that built trust through a blog and friendly Twitter conversations.

According to a report published by Google’s Threat Analyst Group on Monday, North Korean hackers posed as researchers and ran a blog with original content about security vulnerabilities. The hackers circulated their articles and chatted with other researchers through Twitter, started conversations on other platforms and invited security professionals to collaborate. When researchers accepted their offer, the hackers then sent malware-infected files.

“We are talking about a