-Do you use tor or did your brother use it?
-Do you a good anti virus installed ,is your firewall active ?
-What browser do you use ?
-Do you mind showing us a screenshot ?
Its quite some answers for this situation that name TOR has to do with it. I think if you use TOR not as you should you can get any malware or keylogger as long as you are using Windows. I would like to point out that , when anyone uses TOR, don't open up any other browser for clear web together with TOR already running. TOR is made to be run by only itself if you wanna do your job without risking to get your computer infected.
Regarding antivirus and firewall they cannot stop all the malware unfortunately, but I hope OP as you are asking tells us more details. This is an interesting case to me.