The direct meaning of the term 'trojan horse-virus' does not exist. That is because a virus replicates and a trojan-horse does not. Trojan-horse virus is simply a term used to indicate malicious activity done by a trojan-horse on your computer.
A trojan-horse or trojan is malware that disguises itself as a program that the user thinks will perform a beneficial function, but in reality gives access of the user's system to hackers. Usually it is bundled with other programs that the user is downloading. A hacker does not need to individually download a trojan to a specific computer but can use what is called a port scanner to identify which computers have a trojan already installed to be able to hack into their system. Once a hacker gets into a computer with a trojan-horse installed it can change and/or delete files, download software which can include other malware, keystroke logging, view your passwords and other private information on your computer. The trojan-horse virus can also be spread through chat software like Skype or Yahoo Messenger. Once a trojan is downloaded to your computer it can spread to other files.
There are several different types of Trojans. Some of these include: remote access Trojans (RATs), backdoor Trojans (backdoors), IRC Trojans (IRCbots), and keylogging Trojans. Many Trojan encompass multiple types. For example, a Trojan may install both a keylogger and a backdoor. IRC Trojans are often combined with backdoors and RATs to create collections of infected computers known as botnets.
A trojan-horse is significantly different from a worm or virus because it does not self-replicate. It is important to understand the difference between a virus, worm and trojan to be able to diagnose and treat your computer properly. With a virus, a specific file is infected and thus the file would need to be cleaned. Where as for a worm or trojan, the program or file that is causing the problem must be removed or deleted. The problem would persist if it were simply cleaned.
The best way to avoid a trojan-horse virus is by not opening any email attachments from unknown users. Of course there is still a chance of receiving infected attachments from known users. That is why it is advisable that in order to prevent from getting a Trojan-horse virus, you install anti-virus programs such as avast!, Avira or Norton and update them as necessary.
There are also a few steps you can take to recover after being infected by a trojan-horse virus:
1) Contact IT support, if it is available to you
2) Disconnect from the internet, by either disconnecting network cables or disabling your wireless connection.
3) Make sure you backup important files like videos, pictures and other documents. If a Trojan-horse virus is not treated in time it will result in a crash. By backing up important files, you can prevent loss of significantly important information.
4) If none of the above seem to work, you can always try to reinstall the operating system. For some, this is best to be taken to a professional.
Once you have restored your computer, remember:
*Do not open email attachments from senders you do not know.
*Install and update an anti-virus program
*Maintain a firewall on your computer
*Keep your internet connection secure