Bug Classification

An unexpected behavior of any functionality which is not supposed to do is known as software bug  or in simple words we can say bug is Deviation from the expected result. Bug can be categorized into different types basing on the core issues they address.  We can divide into four major criteria. These criteria is-

Interface Related Bugs (UI Bug)/Cosmetic Issues:   As the name suggests, the bugs deal with problems related to UI.  Usually UI related bug are considered less severe.
Examples:

• Improper error/warning/UI messages
• Broken Links
• Spell Mistakes
• Background Color, Alignment Issue

Functionality Related Bugs: Bugs that produce an unexpected/illogical application behavior where the end result differs from the expected result, this type of bug affect the functionality of the application.
Examples:

• Searching of any item leads wrong result Buttons like Save, Delete, Cancel not performing their intended functions 
• A missing functionality (or) a feature not functioning the way it is intended t Continuous execution of loops

Security Related Bugs: Application security defects generally involve improper handling of data sent from the user to the application.  These defects are the most severe and given highest priority for a fix.
Examples:

• Authentication: Accepting an invalid username/password, 
• Authorization: Accessibility to pages though permission not given
• URL rewriting, Cookies editing, Encryption and decryption of important data

Database Related Bugs:  These bugs are deals with improper handling of data in the database. Some time these are due to the improper flow of data in database.
Examples:

• Values not deleted/inserted into the database properly
• Improper/wrong/null values inserted in place of the actual values
• Not validating data type and length from front end