Confidentiality is the prevention of the intentional or unintentional
unauthorized disclosure of contents.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the
Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 60.

Users can obtain certificates with various levels of assurance. Here is a list that describe each of them:
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Class 1/Level 1 for individuals, intended for email, no proof of identity For example, level 1 certificates verify electronic mail addresses. This is done through the use of a personal information number that a user would supply when asked to register. This level of certificate may also provide a name as well as an electronic mail address; however, it may or may not be a genuine name (i.e., it could be an alias). This proves that a human being will reply back if you send an email to that name or email address.
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Class 2/Level 2 is for organizations and companies for which proof of identity is required Level 2 certificates verify a user's name, address, social security number, and other information against a credit bureau database.
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Class 3/Level 3 is for servers and software signing, for which independent verification and checking of identity and authority is done by the issuing certificate authority Level 3 certificates are available to companies. This level of certificate provides photo identification to accompany the other items of information provided by a level 2 certificate.
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Class 4 for online business transactions between companies
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Class 5 for private organizations or governmental security
References:
http://en.wikipedia.org/wiki/Digital_certificate veriSign introduced the concept of classes of
digital certificates:
Also see:
Source: TIPTON, Harold F. & KRAUSE, Micki, Information Security Management
Handbook, 4th edition (volume 1), 2000, CRC Press, Chapter 3, Secured Connections to
External Networks (page 54).

Explanation/Reference:
A modem is a device that translates data from digital form and then back to digital for communication over analog lines.
Source: Information Systems Audit and Control Association,
Certified Information Systems Auditor 2002 review manual, Chapter 3: Technical Infrastructure and Operational Practices (page 114).

Explanation/Reference:
This is not a correct notation for an IPv6 address because the the "::" can only appear once in an address.
The use of "::" is a shortcut notation that indicates one or more groups of 16 bits of zeros.
::1 is the loopback address using the special notation
Reference: IP Version 6 Addressing Architecture
http://tools.ietf.org/html/rfc4291#section-2.1

Explanation/Reference:
A polymorphic virus has the capability of changing its own code, enabling it to have many different variants, making it harder to detect by anti-virus software. The particularity of a stealth virus is that it tries to hide its presence after infecting a system. A Trojan horse is a set of unauthorized instructions that are added to or replacing a legitimate program. A logic bomb is a set of instructions that is initiated when a specific event occurs.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter
11: Application and System Development (page 786).