Recently a family friend has been complaining that he has been getting hacked on his home network and that he has been receiving suspicious messages from the attacker. He says that the attacker has been taking all his subscriptions and email details. His friend who specializes in IT said there's nothing going on after checking his connection. He formatted all computers and instructed him to only use a wired network. His friends and family thought he was just going crazy because he has slight mental issues.
He asked me to come to his house and see if I can find anything suspicious (I am a current IT student and have only completed one semester). I did virus scans and cmd checks and found nothing. I installed a top security router (after he requested it) to ease his mind and attempted to add a VPN. As I was adding the VPN, suddenly his computer started to slow down to the point that I could not switch to any tabs or click on any website. At first, I thought that this was just his laptop playing up because it's a few years old. I decided to connect my phone to the network to enter the VPN details and behold I received a suspicious text message saying that I won an eBay voucher. I immediately disconnected from the network and formatted my phone. There's no way this is a coincidence and I am convinced his network is infected.
Is it possible for his network to infect anything it connects to? Even after changing the router and modem?
Can my smartphone (android) still be infected after formatting it? Am I at risk when using it?
What kind of attack can this be and what steps should I take to resolve the issue?