People are lazy by nature. This is true especially as far as choosing passwords are concern. When we sign up for online services such as e-mail, chat, etc. we for the purpose of convenience opt to choose the easier to remember passwords e.g. batman, superman. Moreover, we use this as passwords to all of the sites that require the use of it. After reading this perhaps you may want to reconsider your choices of passwords.
One method of hacking is called brute forcing wherein a certain software tries to guess the password you are using by matching it with a wordlist. A wordlist is a text file, which is a list of passwords commonly used by people.
Bottom line is don’t use ordinary passwords. It would be better if you use a combination of lowercase and uppercase letters, and numbers. X25sUpErMan34 for example would be a good password. Furthermore, another safety measure would be to use different passwords for different sign ups. Imagine if a hacker were able to hack your password for yahoo and you used the same password for hotmail then you probably would have guessed what would happened.
Another security tool is installing a firewall. There are several freeware firewalls in the web today. Search for one in search engines (google, yahoo) and look at software reviews to see which is the better one to use. Configured correctly, firewalls will protect you from portscan, denial of service attacks, Trojans, etc.