Win32.Sdbot

A trojan is a program that is disguised as legitimate software but is designed to carry out some harmful actions on the infected computer.

Unlike viruses and worms, trojans don’t replicate but they can be just as destructive.

These days trojans are very common. Trojans are divided into a number different categories based on their function or type of damage.

Worms are generally considered to be a subset of viruses, but have key differences. Unlike a virus, a worm is a computer program that replicates, but does not infect other files. Instead, a worm installs itself on a computer and then looks for a way to spread to other computers.

From a user’s perspective, there are noticeable differences. The longer a virus goes undetected, the more files it will infect on the victim computer. By contrast, there is just a single instance of the worm code on the computer.

Like viruses, worms are often subdivided according to the methods they use to infect a system. E-mail worms are distributed as attachments to e-mail messages. IM worms are attached to messages sent with instant messaging programs (such as IRC or ICQ). P2P (peer-to-peer) worms use file-sharing networks to spread. Network worms spread directly over the LAN (Local Area Network) or across the Internet, often exploiting a specific vulnerability.

Of all trojans, backdoor trojans pose the greatest danger to users’ PCs because they give their authors remote control over infected computers. They are downloaded, installed, and run silently, without the user’s consent or knowledge. Upon installation, backdoor trojans can be instructed to send, receive, execute and delete files, gather and transfer confidential data from the computer, log all activity on the computer, and perform other harmful activities.

A DoS (Denial of Service) attack is designed to disrupt or stop the normal running of a Web site, server, or other network resource. Hackers or malware writers resort to various ways to achieve this. A DoS attack can commonly result in a server being flooded with more network traffic than it is capable of processing. This hinders or prevents the server’s normal operation and sometimes causes its complete failure.

Unlike a DoS attack, a DDoS attack employs multiple PCs. The hacker or malware writer normally uses one infected computer - “master” - to centrally coordinate the attack across other, so-called “zombie”, computers. Typically, the malware writer gains control of both master and zombie computers by exploiting a weakness in an application or the operating system on those computers, in order to install a trojan or other malicious code.