Adware is a program that monitors or spies on what computer users do on their computers. They then automatically install advertisements onto the computer.

Spyware and adware are similar indeed. The only difference between the two is that adware does not report to the company, instead it bypasses that and automatically loads the ads onto the computer.

The more adware or spyware that is loaded onto the computer, the longer it takes for the machine to go through its start up process. New toolbars appear in the browser. The homepage is changed and cannot be changed back. Pop-ups will not go away when the computer is running. It can slow your machine and your level of productivity down.

While you may not realize spyware has been installed on your computer, there are some signs to look for. If you notice any changes to your Web browser that you did not make — such as extra toolbars or different homepage settings — as well as changes to your security settings and favorites list, you could have spyware running on your system.

A boot sector virus does not need to be able to successfully boot the victims computer to infect it. Because of this, even non-bootable media can spread a boot sector virus.

Once the infected computer successfully boots, the boot sector virus stays in memory and infects floppies and other media when they are written to by the infected computer.

Boot sector viruses have become increasingly less common as floppy disks have become rarer.

Most malware programs will reinstall themselves even after you think they have been removed. They typically hide deep within the Windows registry, making them difficult to manually remove. When this occurs, your computer may become so unstable that installing a malware removal tool may be impossible.

Anti-virus programs are good protection when kept up to date. However, they frequently miss certain types of malware, such as Trojans and spyware, so it is a good idea to run at least one anti-adware program in conjunction with anti-virus.

Trojan horses spread when people are lured into opening a program because they think it comes from a legitimate source. Trojan horses can also be included in software that you download for free. Never download software from a source that you don’t trust.

A Trojan Horse is full of as much trickery as the mythological Trojan Horse it was named after. Just as the mythological Trojan horse appeared to be a gift, but turned out to contain Greek soldiers who overtook the city of Troy, today's Trojan horses are computer programs that appear to be useful software, but instead they compromise your security and cause a lot of damage. A recent Trojan horse came in the form of an e-mail that included attachments that claimed to be Microsoft security updates, but turned out to be viruses that attempted to disable antivirus and firewall software.

When a Trojan is activated on your computer, the results can vary. Some Trojans are designed to be more annoying than malicious (like changing your desktop, adding silly active desktop icons) or they can cause serious damage by deleting files and destroying information on your system. Trojans are also known to create a backdoor on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised.

Added into the mix, we also have what is called a blended threat. A blended threat is a sophisticated attack that bundles some of the worst aspects of viruses, worms, Trojan horses and malicious code into one threat.. Blended threats use server and Internet vulnerabilities to initiate, transmit and spread an attack. This combination of method and techniques means blended threats can spread quickly and cause widespread damage. Characteristics of blended threats include: causes harm, propagates by multiple methods, attacks from multiple points and exploits vulnerabilities.

Blended threats are considered to be the worst risk to security since the inception of viruses, as most blended threats require no human intervention to propagate.

The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect. For example, a worm could send out copies of itself to everyone listed in your e-mail address book, and their computers would then do the same, which causes a domino effect of heavy network traffic that can slow down business networks and the Internet as a whole. When new worms are unleashed, they spread very quickly. They clog networks and possibly cause a long wait for you (and everyone else) to view Web pages on the Internet.

Worms are often used to drain computer resources such as memory and network access, simply by replicating on a large scale. In addition, worms sometimes delete data and spread rapidly via e-mail.

A worm called Code Red made huge headlines in 2001. This worm could clog the Internet so effectively that things would completely grind to a halt. The Blaster Worm has been designed to tunnel into your system and allow malicious users to control your computer remotely.

A worm usually exploits some sort of security hole in a piece of software or the operating system. For example, the Slammer worm (which caused mayhem in January 2003) exploited a hole in Microsoft's SQL server. A worm called Storm, which showed up in 2007, immediately started making a name for itself. Storm uses social engineering techniques to trick users into loading the worm on their computers.