Certificate (digital certificate, public key certificate): A certificate uses a digital signature to bind a public key to an identity. If the browser encounters a certificate that has not been signed by a trusted certificate authority, it issues a warning to the user. Some organizations create and sign their own certificates, which determines browsers to issue a warning and allow the user to decide whether or not to accept the certificate.

Certificate Authority (CA): An entity that issues certificates and certifies that a public key belongs to a particular identity (website). A list of trusted CAs is stored in the browser. Sometimes a certificate may be issued to fraudulent websites by a CA without rigorous verification processes.

HTTPS: Web browsers use "HTTPS", rather than "HTTP" as URL prefix to indicate that HTTP is sent over a secure link (SSL/TLS). Secure Sockets Layer (SSL) and Transport Layer Security (TLS) are cryptographic protocols used to provide authentication and secure communications over the Internet. SSL/TLS authenticates a server by verifying that the server holds a certificate that has been digitally signed by a trusted certificate authority. It also allows the client and server to agree on an encryption algorithm for securing communications.

Email headers: The headers of an email message represent detailed information about the message you are viewing, such as the IP address from which the message was sent, the return path of that message in case you reply to it, the true email address that sent the message etc.

Below are some tips on how to view headers for some web-based email services and email clients:

Hotmail (web-based email):
- Go to Options > Preferences
- Scroll down to Headers, then click on Advanced Headers

Yahoo! Mail (web-based email):
- Open the message
- Click the Full Headers link within the menu and the full headers will be displayed

Microsoft Office Outlook (email client):
- Right-click the message and choose Options
- Or open the message, go to View and select Options

Outlook Express (email client):
- Right-click the message and select Properties
- Choose the Details tab and click the Message Source button

Mozilla Thunderbird (email client):
- Click to select the email message
- Go to View and click on Message Source
- A new window will appear displaying the full unformatted message