When I upgraded from Windows 8.1 to Windows 10, the Kaspersky program required an upgrade. After that upgrade, the Kaspersky icon didn't appear in the tray either. However, I found it in the "show hidden icons" popup window. So I simply dragged it from that popup window into the tray and that fixed the issue. I didn't have to reinstall Kaspersky to do this. So look in the "hidden icons" popup window (bottom right of tray) and if the icon is there, just drag it into the tray. Hope this helps.