Fortunately, many antivirus programs, as well as comprehensive security software, exist to prevent the effects of software threats. A comprehensive security suite will have specific anti-spyware and dedicated adware removal software and provides general protection from viruses. Most vendors also issue patches that close down vulnerabilities exploited by email viruses. If you use and update good security software, stick to reputable websites and open only files sent to you by senders you know and marked as “safe” by your email provider, you should be able to avoid most threats. (Keep in mind, though, that email accounts are sometimes hacked and used to send spam, so treat even email from people you know with caution.)
With an increasing reliance on mobile devices it is important to be aware of new and emerging software threats that target them specifically. Mobile viruses, for example, can infect one cellular phone and then spread to other devices via the mobile phone network. Bluejacking is the sending of unwanted or unsolicited messages to strangers via Bluetooth technology. It can be a serious problem if obscene or threatening messages and images are sent. Bluesnarfing is the actual theft of data from Bluetooth enabled devices (including both mobile phones and laptops): contact lists, phonebooks, images and other data may be stolen in this way. 
Mobile devices can be infected by viruses that spread themselves via the mobile phone network. These have been a limited threat to date due to the fact that mobile phones use many different operating systems, but as a small number of systems (such as Android and iOS) become dominant, these viruses will be able to spread more widely. In all other respects these are identical to other computer viruses. 
Bluejacking uses a feature originally intended to exchange contact information to send anonymous, unwanted messages to other users with Bluetooth-enabled mobile phones or laptops. In some cases this is used to send obscene or threatening messages or images, and it could be used to spread malware as well. 
Bluesnarfing is the actual theft of data from Bluetooth enabled devices (especially phones). Like bluejacking it depends on a connection to a Bluetooth phone being available. A Bluetooth user running the right software from a laptop can discover a nearby phone and steal the contact list, phonebook and images etc. Furthermore, your phone’s serial number can be downloaded and used to close the phone. Again, the only current defense is to turn your Bluetooth off by setting it to “undiscoverable”. 
Most email viruses rely on the user double clicking on an attachment. This runs a malicious code that mails itself to other users from that computer. Any attachment that you open on your computer could contain a virus and infect your computer even if the extension appears to be safe (such as .txt, .doc and .jpg). Some viruses can infect users as soon as they open the email. These viruses may compromise your computer’s security or steal data, but more often they create excessive email traffic and crash servers.  Viruses can also be spread by clicking on links in emails that lead to malware sites.
This type of virus, also known as a document virus, takes advantage of macros (commands embedded in word processing and spreadsheet software that run automatically) to infect your computer. A macro virus can copy itself and spread from one file to another. If you open a file that contains a macro virus it copies itself into the application’s start up files and infects the computer. The next file you open using the same program, and every file thereafter, will become infected; the infection can therefore spread rapidly across a network. 
Boot-sector viruses are mostly spread through infected storage devices such as USB drives. When your computer is turned on the hardware seeks out the boot-sector program, which is the program the computer runs when it starts up. (This is generally located on the hard drive but can also be on a storage device such as a DVD or USB drive.) A boot-sector virus replaces the original boot-sector with its own, modified version. Upon your next start up the infected boot sector is used and the virus becomes active. It can then read or modify any files or programs on your computer. 
This type of intrusive software displays advertisements on your computer. These usually come in the form of banners and pop-ups when an application is in use. Adware can become a serious problem if it installs itself onto your machine: it can hijack your browser (Internet Explorer, Firefox, Chrome or Safari for example) to display more ads, gather data from your Web browsing without your consent and prevent you from uninstalling it. The most common issues with adware is that it can slow down your Internet connection or render you computer unstable as well as distract you and waste your time. 
While technically a form of adware, spyware has as its primary function the collection of small pieces of information without users’ knowledge. One form of spyware, called a keylogger, actually monitors everything you input into your computer. In addition to monitoring your input and Internet surfing habits, spyware can interfere with your control over your computer by installing additional software, redirecting your browser, changing computer settings, and slowing or cutting off your Internet connection. 
General Tips - Most computers come with embedded security features including a firewall. This prevents unknown programs and processes from accessing the system but is not a replacement for anti-virus software. Your firewall can be located and activated from your computer's control panel. Some websites maintained by antivirus vendors offer free online scanning of your entire computer system, but be sure to verify the source: some sites which claim to scan for viruses actually plant malware on your computer.
A cookie is a small text file which is saved on your computer by a website, mainly used as a means for session management, personalization and tracking while surfing the Web. Some cookies can be beneficial, making for a smoother browsing experience: for instance, they can save small pieces of information into memory, such as your name, so that you don’t constantly have to re-enter it on your most frequently visited websites. Cookies are essential to common features of websites such as "shopping carts" (which store your purchasing decisions while you browse an online commerce site such as Amazon). These cookies are usually deleted after you leave the website or within a few days of not visiting it.
Other cookies, however, can be far more of a nuisance. These cookies will recreate themselves after the user has deleted them. A script will then keep this information in some other location on the computer, unbeknownst to the user. Other kinds are able to closely track your online habits and can last up to a year on a given server. 
There are several different types of cookies. Each has different properties:
This type of cookie only lasts for the duration of your stay on a particular website and is deleted when you close your browser.
This type of cookie is also known as a “tracking” or “in memory” cookie. These cookies can last up to a year from each time a user revisits the server.
These cookies are used when you are visiting a secure site (one where the Web address begins with "https" rather than "http"). These cookies are encrypted when being sent to and from your computer and the server, which means that they are more secure if someone intercepts or copies them.
This type of cookie, sometimes referred to as a “zombie” or "super" cookie, automatically recreates itself in some other location on the computer after a user has deleted it.
Browser hijacking is a malicious online activity where hijackers change the default settings in your Internet browser. Links may appear that point to websites you would usually avoid, new toolbars and favorites that you do not want may be added and your computer may slow down overall. Users will also often find themselves unable to return to their original settings once this is done. The purpose of this threat is to force you to visit a website. This increases the traffic and number of “hits” a website receives which allows it to boost its advertising revenue. (These websites may also contain malicious scripts or viruses.) Browser hijackers can be extremely persistent and if they can’t be removed you may find yourself having to reinstall your browser or restore your entire system to its original settings. 
While you are generally safe from malicious scripts if you stick to trusted sites, there have been cases in which hackers installed malicious scripts onto legitimate sites. The only sure way of preventing script attacks is to control which scripts run when you visit a site.
 Tupas, M. (2010). 21 Types of Computer Security Threats. Retrieved from http://www.whatsthelatest.net/news/types-computer-security-threats-cybercrime/
 Beal, V. (2010). What are Cookies and What do Cookies Do?. Retrieved from http://www.webopedia.com/DidYouKnow/Internet/2007/all_about_cookies.asp
 Tupas, M. (2010).