Receiving a Virus

What do you mean by computer "code"?

Running a program you get over the internet is one of the most dangerous things you can do. Unless you know what you are doing, you can easily give the program permission to do whatever it wants.

So yes. If you are talking about running a program, it can bypass your virus scan whether it is received by thumbdrive, received over the internet or downloaded as a file attachment.

Yhe answer is yes and no.
Your anti virus program is usually the first utility to start so it should catch any attempt to install maliciouse code.
That is assuming your antivirus program recognises the code as malicious. In many cases a piece of code that in itself is not malicious on your computer can be inserted via thumb drive or by downloading seemingly innocuouse material from the net. this is then used to secretly download other more maliciouse material.

Keeping your operating system and anti virus up to date via their respective update sites is a most important part of computer maintenance