Viruses and Trojans are types of malicious software or code. They are designed to steal damage and inflict damage on the data, the network, and the computer. Systems can be affected by the malware when they are bundled with other programs or are attached to the macro files. Others damage the operating system, software, and network device. A vast number of malware files are downloaded by downloading an attachment or clicking on an email.

Some of the types of common malware include viruses, Trojans, worms, spyware, ransomware, and bots. Damages may lead to pop-up ads, stealing personal information, money, data destruction, and disabling systems. Malware also damage the hardware of PCs.

While referring to a computer virus, most people use viruses and Trojans interchangeably. However, they are not the same. Viruses and Trojan horses are all malicious programs and cause damage to the computer.

Trojans
A Trojan or Trojan horse is not a virus, but a type of malware that presents itself as legitimate software. It is used by hackers and cyber thieves to gain access to the user’s system by tricking them into downloading the Trojan. Trojans open back-door access into your computer system, allowing them to go through your personal and confidential information. Trojans do not replicate or infect other files.

At a glance, a Trojan will look like a useful software file. However, it will damage the computer software once it is run and installed on the computer. Some Trojans can cause serious damage like deleting files and information. The back door allows personal information to be used and gives malicious access. You need to take the following steps to protect your computer from Trojans:

• Updating the operating system
  This is important if you work on a Microsoft Windows system. Install antivirus software and download updates. The updates ensure the computer is protected from viruses, Trojans, and worms. Make sure that the antivirus scans emails and various files that are downloaded from the web. This helps prevent malware programs from accessing your computer.
• Using a firewall
  Installing a firewall prevents unauthorized access to your system. The firewall can be a software or hardware. The hardware firewall provides a strong protection from different form of attacks. This can be bought as part of broadband routers or a standalone product, but is not effective in battling Trojans and viruses. A software firewall, on the other hand, is far more effective in checking emails and network traffic. For home computer users, a software firewall works best. It protects the computer from unauthorized external attempts to gain access to your computer. It also provides added protection against e-mail worms and common Trojan programs. The software firewall, however, protects only the system it is installed on. The firewall, along with good antivirus scanning software, it adds extra security for the computer. 

Virus
A virus attaches to a program and then spreads from one computer to another, leaving each computer affected. The range of severity can be from mild to completely damaging. It can damage the software and hardware of a system. The virus attaches to the executable file, this file cannot affect the computer unless it is opened and run. Sharing an infected file will spread the virus.

Code Red was a blended threat, having defaced web servers and having launched DOS attacks. In fact, the Code Red II, a variant of the former, was left behind in the system Trojan horses for execution later on. CodeRed was built into the memory and not on the hard disk which would allow the Trojan to slip. It was estimated that CodeRed cost the world $2.6 billion.