wifi security

I agree with Tony. The behavior of what is being described can only happen by user interaction. The fact your wireless network was not secured has not bearing on your situation. Had you said your ISP reported illegal activity originating from your network, then that would be a situation where your unsecured network would have contributed to this if no one in your household were engaged in that activity.

If your antivirus software isn't picking up the compromise on your computer, you'll have to take steps to remediate your computer.