"Malware" is short for malicious software and used as a single term to refer to virus, spyware, worm etc. Malware is designed to cause damage to a stand alone computer or a networked pc. So wherever a malware term is used it means a program which is designed to damage your computer it may be a virus, worm or Trojan.

Worms:-
 Worms are malicious programs that make copies of themselves again and again on the local drive, network shares, etc. The only purpose of the worm is to reproduce itself again and again. It doesn’t harm any data/file on the computer. Unlike a virus, it does not need to attach itself to an existing program. Worms spread by exploiting vulnerabilities in operating systems

Examples of worm are: - W32.SillyFDC.BBY
 Packed.Generic.236
 W32.Troresba

Due to its replication nature it takes a lot of space in the hard drive and consumes more cpu uses which in turn makes the pc too slow also consumes more network bandwidth.

Virus:-
Virus is a program written to enter to your computer and damage/alter your files/data. A virus might corrupt or delete data on your computer. Viruses can also replicate themselves. A computer Virus is more dangerous than a computer worm as it makes changes or deletes your files while worms only replicates itself with out making changes to your files/data.

Examples of virus are: - W32.Sfc!mod
 ABAP.Rivpas.A
 Accept.3773

Viruses can enter to your computer as an attachment of images, greeting, or audio / video files. Viruses also enters through downloads on the Internet. They can be hidden in a free/trial softwares or other files that you download.

So before you download anything from internet be sure about it first. Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it actually cannot infect your computer unless you run or open the malicious program. It is important to note that a virus cannot be spread without a human action, such as running an infected program to keep it going.

Virus is of different types which are as follows.

1) File viruses
 2) Macro viruses
 3) Master boot record viruses
 4) Boot sector viruses
 5) Multipartite viruses
 6) Polymorphic viruses
 7) Stealth viruses

File Virus:-This type of virus normally infects program files such as .exe, .com, .bat. Once this virus stays in memory it tries to infect all programs that load on to memory.

Macro Virus: - These type of virus infects word, excel, PowerPoint, access and other data files. Once infected repairing of these files is very much difficult.

Master boot record files: - MBR viruses are memory-resident viruses and copy itself to the first sector of a storage device which is used for partition tables or OS loading programs .A MBR virus will infect this particular area of Storage device instead of normal files. The easiest way to remove a MBR virus is to clean the MBR area,

Boot sector virus: - Boot sector virus infects the boot sector of a HDD or FDD. These are also memory resident in nature. As soon as the computer starts it gets infected from the boot sector.
 Cleaning this type of virus is very difficult.

Multipartite virus: - A hybrid of Boot and Program/file viruses. They infect program files and when the infected program is executed, these viruses infect the boot record. When you boot the computer next time the virus from the boot record loads in memory and then start infecting other program files on disk

Polymorphic viruses: - A virus that can encrypt its code in different ways so that it appears differently in each infection. These viruses are more difficult to detect.

Stealth viruses: - These types of viruses use different kind of techniques to avoid detection. They either redirect the disk head to read another sector instead of the one in which they reside or they may alter the reading of the infected file’s size shown in the directory listing. For example, the Whale virus adds 9216 bytes to an infected file; then the virus subtracts the same number of bytes (9216) from the size given in the directory.

Trojans: - A Trojan horse is not a virus. It is a destructive program that looks as a genuine application. Unlike viruses, Trojan horses do not replicate themselves but they can be just as destructive. Trojans also open a backdoor entry to your computer which gives malicious users/programs access to your system, allowing confidential and personal information to be theft.

Example: - JS.Debeski.Trojan

Trojan horses are broken down in classification based on how they infect the systems and the damage caused by them. The seven main types of Trojan horses are:
• Remote Access Trojans
• Data Sending Trojans
• Destructive Trojans
• Proxy Trojans
• FTP Trojans
• security software disabler Trojans
• denial-of-service attack Trojans

Adware: - Generically adware is a software application in which advertising banners are displayed while any program is running. Adware can automatically get downloaded to your system while browsing any website and can be viewed through pop-up windows or through a bar that appears on a computer screen automatically. Adwares are used by companies for marketing purpose.

Spywares: - Spyware is a type of program that is installed with or without your permission on your personal computers to collect information about users, their computer or browsing habits tracks each and everything that you do without your knowledge and send it to remote user. It also can download other malicious programs from internet and install it on the computer. Spyware works like adware but is usually a separate program that is installed unknowingly when you install another freeware type program or application.

Spam: - Spamming is a method of flooding the Internet with copies of the same message. Most spams are commercial advertisements which are sent as an unwanted email to users. Spams are also known as Electronic junk mails or junk newsgroup postings. These spam mails are very annoying as it keeps coming every day and keeps your mailbox full.

Tracking cookies: - A cookie is a plain text file that is stored on your computer in a cookies folder and it stores data about your browsing session. Cookies are used by many websites to track visitor information A tracking cookie is a cookie which keeps tracks of all your browsing information and this is used by hackers and companies to know all your personal details like bank account details, your credit card information etc. which is dangerous .

Misleading applications: - Misleading applications misguide you about the security status of your computer and shows you that your computer is infected by some malware and you have to download the tool to remove the threat. As you download the tool it shows some threats in your computer and to remove it you have to buy the product for which it asks some personal information like credit card information etc. which is dangerous.