It is difficult to disagree with the view that spam is an extremely unpleasant thing. When every day your mail box is being flooded with absolutely useless letters it can only be annoying. Apart from that, recently spam has become very dangerous both for the computer and the user. As a matter of fact, a file attached to an e-mail message can be simply opened from the mail client program. And if the attached file is an executable program then it will be run automatically. The danger is that a file from an unknown sender can easily be a virus or contain viruses. Which is more dangerous (but unfortunately not everybody clearly understand this) is that those days when viruses were only .exe or .com files are well in the past. Nowadays viruses can be hidden practically in every type of file including Microsoft Office documents or mp3 audio files.
This is why one of the most important rules in the Internet security now, like washing your hands before you eat, is NOT to open any attachments in letters received form an unknown sender. The best way is to delete such letters immediately but if you have some reasons to believe the letter can contain some information, which is of interest for you, you need to check it using reliable anti-virus software with up-to-date virus databases.
However many reluctant users are often disregarding this rule and doing so they put under risk not only the safety of their computer as a technical device but their own personal security. Many people maybe do not realize but nowadays personal computers store and deal with a huge amount of information which is not meant to be accessed by anyone else but the user.
You can hastily reply to this saying that your computer definitely doesn't contain anything important. And almost always you are wrong. If you are not paying enough attention to the Internet security then the mail clients or web-browsers you use are storing logins ant passwords to your mailboxes (i. e. to your personal correspondence), various login information for forums, blogs, live journals, social networks, such as "MySpace" or "Facebook" and so on. If you are maintaining a web site then your operation system keeps your access passwords for control panel, for payment panel ( where very often it is possible to close the site) and for FTP access. Besides, if you are managing your bank account from your computer or have accounts in electronic payment systems like PayPal, E-Gold, Digital Money then they can also be under threat when somebody gets access to your computer.
Moreover, the violators, who sent a trojan program or keylogger to you, can get access to the data stored on your computer and using the latest available high speed Internet connections they can easily download from your computer practically unlimited amounts of data. In fact, this means that in a short period of time they can obtain literally all the information that you have in your PC. Unfortunately, it is quite easy to get access to your computer especially if you don not care much about the security. It is enough that you just run an "infected" file sent to you by e-mail together with other ordinary spam letters.
Obviously, passwords and other private information are not stored by an operation system or related programs in open access but still for those who know how to deal with them it is not going to be really difficult to extract all the necessary secrets. This is why it is highly recommended NOT to save passwords using built in password saving options. The latest viruses are capable of stealing saved passwords and those who create the viruses and use them have all the necessary means for decoding the stolen information. Of course, different programs using their own authorization procedures have different levels of security and different ways of protecting confidential data. Some responsible software providers (for instance Total Commander developers) are warning the users that although the program has a password saving option it can be insecure to use it and the users must decide to do it on their own risk. Other programs do not produce such warnings but this doesn't necessarily mean that confidential data there are securely protected.
Another thing that you should pay attention to is cookies. These are files that meant to make easier for you to work with forums, blogs and other Internet resources where the authorization is required but at the same time they can also be used to steal your login information.
With all that being said, it is extremely important to pay attention to Internet security but on the other hand, there is no reason to get paranoid. Criminals in general and Internet criminals in particular usually targeting careless victims. Even if the users follow just some basic rules of "Internet hygiene" it becomes more difficult and time consuming to access their private data. This is why the first rule of "Internet hygiene" is to be careful. Do not neglect spam filtering options available on mail servers or in your e-mail client. Delete immediately all the spam letter that managed to get into your Inbox. Never try to open attachments in the letters that you received from an unknown user and even if the letter was sent to you by your friend or trusted correspondent, still check it using anti-virus program, especially if you did not expect the letter. You have to realize that nowadays viruses can attach themselves to outgoing messages without the sender being aware.
In general, a reliable anti-virus software with an up-to-date virus database must be always in active state in order to be able to immediately detect and neutralize the activity of viruses and various trojan programs when they are trying to get access to your computer via e-mail client or while you are visiting an "infected" web-site. Of course, the absolute security of your private data stored on the computer can be guaranteed only when the computer is disconnected from the Internet but even just following some basic rules and simply taking care you can securely protect your computer and your privacy.