According to the story above, Alex is only in contact stage with the alleged or to-be partners. What really happened, did he disclose his private details at the course of the meeting?
Could it be that they hosted the meeting with tools like TeamViewer and he gave them unrestricted access to his computer?
I think they might sent him a file that contain malware, told him to open it. He trusted them and think the file is safe. But when he will know, it would have already been late. I have a separate device that I am using to open files, download things and I do not have banks, exchanges and wallets apps on the device.