A majority of the security breaches over the past 2-3 years have been a targeted attack that started with an email. Before you open an email with links, or even a document, make sure that you verify the source. Email is a way you can be tricked to download spyware and malware which can compromise your machine. Also, never click on a link from your bank in an email. It is much better to go directly to the website and enter the appropriate information.