Phoning home
Encyclopedia
Phoning home, in computing, refers to an act of client
to server
communication where a client device or client application software reports its location on a network, the currently logged on user, or any other information to a server computer. Generally the user and/or proprietor of the device or software do not want this kind of communication behind his back.
Phoning home may be useful for the proprietor in tracking a missing or stolen computer. This type of phoning home is frequently used on mobile computers at corporations. It typically involves a software agent which is difficult to detect or remove. However, there are malicious types of phoning home such as surreptitious communication between applications or hardware installed at end-user sites and their manufacturers or developers. The traffic may be encrypted
to make it difficult or impractical for the end-user to ascertain what data is being transmitted.
Phoning home could be for purposes of access control, such as transmitting an authorization key. This is done with the Adobe Creative Suite. Each time one of the programs is opened, it phones home with the serial number. If the serial number is listed as being already in use, or a fake, then the program will present the user with the option of inputting the correct serial number. If the user refuses, the next time the program loads, it will operate in trial mode until a valid serial number has been input. However, the method can be thwarted by either disabling the internet
connection when starting the program or adding a firewall
or Hosts file rule to prevent the program from communicating with the verification server.
Phoning home could also be for marketing purposes, such as the "Sony BMG Rootkit", which transmits a hash of the currently playing CD back to Sony, or a digital video recorder
(DVR) reporting on viewing habits. High-end computing systems such as mainframes
have had 'phone home' capabilities for many years, to alert the manufacturer of hardware problems with the mainframes or disk storage subsystems (this enables repair or maintenance to be performed quickly and even proactively under the maintenance contract).
Aside from malicious software phoning home, phoning home may be done to track computer assets—especially mobile computers. One of the most well-known software applications that leverages phoning home for tracking is Absolute Software's CompuTrace. This software employs an agent which calls into an Absolute-managed server on regular intervals with information companies or the police can use to locate a missing computer.
file tries phoning (to its author's) home.
HTML
e-mail
messages can can easily implement a form of "phoning home". Images and other files required by the e-mail body may generate extra requests to a remote web server
before they can be viewed. The IP address
of the user's own computer is sent to the web server (an unavoidable process if a reply is required), and further details embedded in request URLs can further identify the user by e-mail address, marketing campaign etc. Such extra page resources have been referred to as "web bug
s" and they can also be used to track off-line viewing and other uses of ordinary web pages. So as to prevent the activation of these requests, many e-mail client
s do not load images or other web resources when HTML e-mails are first viewed, giving users the option to load the images only if the e-mail is from a trusted source.
applications that "phone home" to gather and store information about a person's machine. For example, the Pushdo Trojan shows the new complexity of modern Malware applications and the phoning home capabilities of these systems. Pushdo has 421 executables available to be sent to an infected Windows client.
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
to server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
communication where a client device or client application software reports its location on a network, the currently logged on user, or any other information to a server computer. Generally the user and/or proprietor of the device or software do not want this kind of communication behind his back.
Phoning home may be useful for the proprietor in tracking a missing or stolen computer. This type of phoning home is frequently used on mobile computers at corporations. It typically involves a software agent which is difficult to detect or remove. However, there are malicious types of phoning home such as surreptitious communication between applications or hardware installed at end-user sites and their manufacturers or developers. The traffic may be encrypted
Encryption
In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
to make it difficult or impractical for the end-user to ascertain what data is being transmitted.
Non-illegal phoning home
There are some uses for the phoning home practice that are legal in some countries, for example:Phoning home could be for purposes of access control, such as transmitting an authorization key. This is done with the Adobe Creative Suite. Each time one of the programs is opened, it phones home with the serial number. If the serial number is listed as being already in use, or a fake, then the program will present the user with the option of inputting the correct serial number. If the user refuses, the next time the program loads, it will operate in trial mode until a valid serial number has been input. However, the method can be thwarted by either disabling the internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
connection when starting the program or adding a firewall
Firewall (computing)
A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....
or Hosts file rule to prevent the program from communicating with the verification server.
Phoning home could also be for marketing purposes, such as the "Sony BMG Rootkit", which transmits a hash of the currently playing CD back to Sony, or a digital video recorder
Digital video recorder
A digital video recorder , sometimes referred to by the merchandising term personal video recorder , is a consumer electronics device or application software that records video in a digital format to a disk drive, USB flash drive, SD memory card or other local or networked mass storage device...
(DVR) reporting on viewing habits. High-end computing systems such as mainframes
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
have had 'phone home' capabilities for many years, to alert the manufacturer of hardware problems with the mainframes or disk storage subsystems (this enables repair or maintenance to be performed quickly and even proactively under the maintenance contract).
Aside from malicious software phoning home, phoning home may be done to track computer assets—especially mobile computers. One of the most well-known software applications that leverages phoning home for tracking is Absolute Software's CompuTrace. This software employs an agent which calls into an Absolute-managed server on regular intervals with information companies or the police can use to locate a missing computer.
More phone-home uses
Other than phoning to the home (website) of the applications' authors, applications can allow their documents to do the same thing, thus allowing the documents' authors to trigger (essentially anonymous) tracking by setting up a connection which is intended to be logged. Such behavior, for example, caused v7.0.5 of Adobe Reader to add an interactive notification whenever a PDFPortable Document Format
Portable Document Format is an open standard for document exchange. This file format, created by Adobe Systems in 1993, is used for representing documents in a manner independent of application software, hardware, and operating systems....
file tries phoning (to its author's) home.
HTML
HTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
E-mail
Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...
messages can can easily implement a form of "phoning home". Images and other files required by the e-mail body may generate extra requests to a remote web server
Web server
Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
before they can be viewed. The IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
of the user's own computer is sent to the web server (an unavoidable process if a reply is required), and further details embedded in request URLs can further identify the user by e-mail address, marketing campaign etc. Such extra page resources have been referred to as "web bug
Web bug
A web bug is an object that is embedded in a web page or e-mail and is usually invisible to the user but allows checking that a user has viewed the page or e-mail. One common use is in e-mail tracking. Alternative names are web beacon, tracking bug, and tag or page tag...
s" and they can also be used to track off-line viewing and other uses of ordinary web pages. So as to prevent the activation of these requests, many e-mail client
E-mail client
An email client, email reader, or more formally mail user agent , is a computer program used to manage a user's email.The term can refer to any system capable of accessing the user's email mailbox, regardless of it being a mail user agent, a relaying server, or a human typing on a terminal...
s do not load images or other web resources when HTML e-mails are first viewed, giving users the option to load the images only if the e-mail is from a trusted source.
Malicious phoning home
There are many MalwareMalware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...
applications that "phone home" to gather and store information about a person's machine. For example, the Pushdo Trojan shows the new complexity of modern Malware applications and the phoning home capabilities of these systems. Pushdo has 421 executables available to be sent to an infected Windows client.