There is an article at
http://www.computerweekly.com/Article123086.htm worth reading.
Passwords are something that many users don't take seriously enough. Many people use the same password for everything on the net that needs a password and that leaves them very vulnerable. You only need someone on a site you have used with access to users passwords and they could try your logon details on other similar sites to see if they work and if they do then try them on internet banking sites.
Try to use a different login name and password on every site you use, although it can be helpful if you are posting on several forums dealing with similar topics to have the same username but always have a different password. Make passwords hard to guess with a combination of letter and numbers. This is also worth doing with email addresses to prevent spam where you are torn between security and making them easy to remember.
Some trojans put a keylogger on your system which can record your passwords so make sure that your Antivirus is up to date and firewall is set up correctly. What I do is to use AiRoboform to store part of the passwords and complete them manually after AiRoboform has inserted its part. This can thwart keyloggers, but the main thing is to prevent them getting on your system in the first place. One of the main ways that you can be infected is via email so there is a little trick that can prevent your system, and those of your friends if you tell them about it, from being used to relay trojans. Set up a contact in your address book with the name !000 and an email address of WORM ALERT !!!!!!!! . If a worm tries to replicate using the names in your address book it will fail to send to any of them with that in the list of recipients.
It is worth remembering that URLs can appear to be those of reputable organisations but there are many ways of masking the true identity of the site. Have a read of
http://www.pc-help.org/obscure.htm to see more about URLs.