If someone uses a RAT or something of the sort to gain access to your computer and network, is it possible for them to reroute their internet access through your I.P.? This question is kinda concerning the larger majority of people who have these types of malicious programs installed on their PC without their knowledge. I'd imagine it could be extremely damaging to have a potential criminal rerouting his network through yours (for obvious reasons). If anyone could give me an answer to this is would greatly appreciated, and if anyone has any tips on how to tell if someone is 'rerouting' their internet access through yours, that would also be helpful. Thanks
Routing traffic through a computer is a very simple process that can be done even if the software implementing (it's called a proxy server, by the way) it is not running with specials privileges so the answer is yes. There are some technical complications that might prevent the use of standard software difficult but nothing that cannot be done (and, actually, that is a standard feature
However, asking such a question is similar to wondering if someone who broke into you house could make prank calls to emergency services using your phone: yes, it can be the case but it's hardly the worse of your problems.
With admin/root/... access to a computer, independent of local/remote, it's possible to request any internet sites from this computer, it's possible to save some child porns on it, as well as unlicensed software and/or unpaid movies, etc.etc.
Reliably detecting such things while the computer is still vulnerable is pretty much impossible. Preventing unauthorized access and malware in the first place is the only solution. And avoiding pissing of governments and other influental organizations/people.
Depending on the level of paranoia, you should avoid any hardware from major brands too (or stop using computers at all). Eg. recent CPUs from Intel have remote management stuff builtin (in the CPU itself). While in theory, you need to allow it before anyone can use it, security-relevant bugs and hidden features were found already. As it is a CPU, there is no auto-update, and it works even when the computer is turned off.