As we can see from the discussion in this article, we may face a range of threats that are either set using specialized tools (denial of service, password cracking, packet sniffing) or are implemented by the human factor (social engineering). The widespread usage of hacking tools and the ease with which they can be used to damage are the main factors that cause more and more attacks to be listed everyday. Of course, human innocence (or lack of knowledge) adds to the problem and makes it even bigger. 

We should not take for granted the need for security. Even the most secure system can be damaged by a well organized threat. Therefore we must be alert at all times, waiting for the unexpected.
 
We will continue the discussion of the possible threats you may encounter when using the Internet in the next article.

http://www.cert.org/tech_tips/denial_of_service.html

http://www.cisco.com/warp/public/707/newsflash.html

http://whatis.techtarget.com/definition/
0,289893,sid9_gci213591,00.html

http://searchsecurity.techtarget.com/sDefinition/
0,,sid14_gci557336,00.html

http://eyeonsecurity.org/articles/sniffers.html

http://geodsoft.com/howto/password/cracking_passwords.htm

http://searchsecurity.techtarget.com/sDefinition/
0,,sid14_gci531120,00.html

http://www.nmrc.org/pub/faq/hackfaq/hackfaq-04.html