Phishing campaigns have started to use Basecamp as part of malicious phishing campaigns. Basecamp is a web-based project management solution that allows people to collaborate, chat with each other, create documents, and share files. Security researchers MalwareHunterTeam and James have found that threat actors are distributing Bazar loader using public Basecamp download links. Threat actors can create carefully constructed and targeted campaigns to infiltrate a network as users may feel that the file is from their Basecamp project. Users can be lulled into a false sense of trust and open files that they normally would not.
Source: https://www.bleepingcomputer.com/news/security/hackers-now-abuse-basecamp-for-free-malware-hosting/