How to spread a Trojan Horse: Methods to spread Trojan Horse on Internet ~ Hacks N Cracks

Wanna spread some TROJAN Virus then read below, the modes of transmission..

Modes of Transmission

ICQ
People can also get infected while chatting / talking / video messaging over ICQ or any other Instant Messenger Application. It is a risk that the user undertakes when it comes to receiving files no matter from whom or where it comes.
IRC
Here also, the threat comes from exchange of files no matter what they claim to be or where they come from. It is possible that some of these are infected files or disguised files.
Attachments
Any attachment, even if it is from a known source should be screened as it is possible that the source was infected earlier and is not aware of it.
Physical Access
Physical access to a target machine is perhaps the easiest way for an attacker to infect a machine. The motive may be a prank or just plain curiosity.
Browser and E-mail Software Bugs
Having outdated applications can expose the system to malicious programs such as Trojans without any other action on behalf of the attacker.
NetBIOS (File Sharing)
If port 139 is opened, the attacker can install trojan .exe and modify some system file, so that it will run the next time the system is rebooted. To block file sharing in Windows version, go to: Start->Settings->Control Panel->Network->File and Print Sharing and uncheck the boxes there.