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6.1.8 Potentially unwanted applications

Potentially unwanted applications (PUAs) are not necessarily intended to be malicious, but may affect the

performance of your computer in a negative way. Such applications usually require consent for installation. If they are

present on your computer, your system behaves differently (compared to the state before their installation). The most

significant changes are:

New windows you haven’t seen previously (pop-ups, ads),

Activating and running of hidden processes,

Increased usage of system resources,

Changes in search results,

Application communicates with remote servers.

6.2 Types of remote attacks

There are many special techniques which allow attackers to compromise remote systems. These are divided into several

categories.

6.2.1 DoS attacks

DoS, or Denial of Service, is an attempt to make a computer or network unavailable for its intended users. The

communication between afflicted users is obstructed and can no longer continue in a functional way. Computers

exposed to DoS attacks usually need to be restarted in order to work properly.

In most cases, the targets are web servers and the aim is to make them unavailable to users for a certain period of time.

6.2.2 DNS Poisoning

Using DNS (Domain Name Server) poisoning, hackers can trick the DNS server of any computer into believing that the

fake data they supplied is legitimate and authentic. The fake information is cached for a certain period of time, allowing

attackers to rewrite DNS replies of IP addresses. As a result, users trying to access Internet websites will download

computer viruses or worms instead of their original content.

6.2.3 Worm attacks

A computer worm is a program containing malicious code that attacks host computers and spreads via a network. The

network worms exploit security vulnerabilities in various applications. Due to the availability of the Internet, they can

spread all over the world within a few hours of their release. In some cases, even in minutes.

Most worm attacks (Sasser, SqlSlammer) can be avoided by using default security settings in the firewall, or by blocking

unprotected and unused ports. Also, it is essential that your operating system is updated with the most recent security

patches.

6.2.4 Port scanning

Port scanning is used to determine which computer ports are open on a network host. A port scanner is software

designed to find such ports.

A computer port is a virtual point which handles incoming and outgoing data – this is crucial from a security point of

view. In a large network, the information gathered by port scanners may help to identify potential vulnerabilities. Such

use is legitimate.

Still, port scanning is often used by hackers attempting to compromise security. Their first step is to send packets to

each port. Depending on the response type, it is possible to determine which ports are in use. The scanning itself

causes no damage, but be aware that this activity can reveal potential vulnerabilities and allow attackers to take control

of remote computers.

Network administrators are advised to block all unused ports and protect those that are in use from unauthorized

access.

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