Trojans by name should tell you that it could be anything that causes the problem. A trojan is a virus posing as something else, contrary to popular belief, it does not have to be .exe to cause problems, a binding program is used by trojan makers so add a virus to a regular file and when the regular file is executed ( in this case probably when you play the music track ) it will install the virus at the same time.
No virus software is 100% effective, and tend to fend off against well known or very generic viruses, if it's a teenager locked in his bedroom trying to cause a bit of trouble odds are the scanner wont find it as the virus will be unique.
So basically, the internet as a whole isn't safe, if a pro-hacker wanted to he could get into your computer and there is nothing you could do about stopping him. What there are is varying levels of security, never downloading files etc reduces the risks of contracting a virus, however this is impractical. What is a FACT is that a file sharing program increases the risk of contracting a virus greatly. A file sharing program is basically a program that constantly shouts out "I'm here, I've got this!" to anyone who wants to listen and the file sharing program provides a direct link for others to your computer and therefore it is common sense that without this shouting or the direct link your computer is a lot safer.
A very long winded and unorganised reply but I think you get the point
