Windows Boot file on Mac

A friend of mine downloads a lot of stuff and had it all on a memory stick. One of them was a Windows boot file he had downloaded, and I needed to transfer some files to him so he used his memory stick.

I don't know where he got the boot file from. I didn't open it, I just transferred my stuff on to the memory stick then removed it. I didn't run anything.

If the files on his memory stick weren't 'clean', or had something on the memory stick that shouldn't have been, could my MacBook be infected with anything, or is it most likely clean?

Also, while am at it. Is is possible for an email account, Facebook account, or Twitter account to actually have a virus? Or is that not possible? It's just I logged on to my Twitter and Facebook after the memory stick had been in my machine, now am wondering if they're still 'clean accounts'? This might be a stupid question, but I figured I'd ask whilst am here.

 

I'm not sure if it was an ISO or something along those lines. I didn't open the folder it was in.

According to my friend, it's a file needed to boot into Windows - he deleted it when he removed his partition of Windows 8 accidentally, so couldn't start into 7.