Do not use your primary e-mail address for online submissions.
Using your e-mail address when filling out a form online often results in your e-mail address being spammed. Consider opening an additional e-mail address from a free provider, such as Yahoo or Hotmail, to use when filling out online forms. Make sure you log into these accounts regularly, though, or they will be cancelled.
Do not send personal information through e-mail.
E-mail is not very secure or private. Once you send someone a message, you have no control over what happens to it after it leaves your computer. Think of it as sending a postcard written in pencil. As the card is delivered, it makes numerous stops and can be altered or read by various people. Personal information should never be sent via e-mail. Do not send anything over e-mail that you would not want everyone to see.
Beware of sites that offer some sort of reward or prize in exchange for your contact information or other personal details.
There's a very high probability that they are gathering this information for direct marketing purposes (or spam). In many cases, your name and address are sold to other marketers (who in turn do the same). Be especially wary of sweepstakes and contests. You probably won't win, but the marketer will make money from selling your information.
Do not reply to unsolicited e-mail (spam) for any reason.
If you get a spammed advertisement, don't take the sender up on whatever offer they are making, and don't bother to follow the unsubscribe instructions you've been given. This simply confirms that your address is being read by a real person, and you'll find yourself on dozens more spammers' lists in no time.
Do not read spam.
Some spam e-mails automatically send a return receipt to the spammer telling them that you opened their message, which will probably cause them to send you more spam. When you receive spam, delete it instead of reading it.
Be wary of attachments.
Do not open an attachment unless you trust the sender. Most viruses and Trojans are spread through e-mail attachments.
If you do not know the sender, it is best to delete the attachment. If you think the attachment may be legitimate, contact the sender and ask about the contents of the attachment before you open it. If you do not receive a reply, do not open the e-mail message.
Do not install any software patches that were sent to you via e-mail.
Most reputable vendors have security-verified Web sites from which you can download software patches.
Do not give phishers any information.
Phishing is a scam where the perpetrator sends out legitimate-looking e-mails appearing to come from some of the Web's biggest sites, including eBay, PayPal, MSN, Yahoo, Best Buy and America Online, in an effort to phish (pronounced "fish") for personal and financial information from the recipient.
Here’s an example of how it might work: You get a message from your bank that asks you to update your account information. You click on the link, the legitimate bank site opens, then a page opens up on top asking you for your account info. This info page does not belong to the legitimate site. If you fill out your personal information and submit it, the information will go to the “phisher” to be sold or used to steal your identity.
Some phishers are very good at making fake Web sites look legitimate. So it is best not to give out this personal information over the Web, especially if you were notified through an e-mail message. If you are unsure of what to do, contact the institution about the authenticity of the site before you give out any personal information.
Remember: when in doubt, delete.
Source: searchSecurity.com Definitions