Mobile code

In computer science, mobile code is software transferred between systems, e.g. transferred across a network or via a USB flash drive, and executed on a local system without explicit installation or execution by the recipient. Examples of mobile code include scripts (JavaScript, VBScript), Java applets, ActiveX controls, Flash animations, Shockwave movies (and Xtras), and macros embedded within Office documents.

Mobile code can also download and execute in the client workstation via email. Mobile code may download via an email attachment (e.g., macro in a Word file) or via an HTML email body (e.g., JavaScript). For example, the ILOVEYOU, TRUELOVE, and AnnaK email viruses/worms all were implemented as mobile code (VBScript in a .vbs email attachment that executed in Windows Scripting Host).

In almost all situations, the user is not aware that mobile code is downloading and executing in their workstation.

Mobile code technologies can be used to support three different paradigms:

• Code on demand,
• Remote evaluation, and
• Mobile agents.

Mobile code technologies can be used to download and execute malicious code in client workstations via email and via visiting Web pages on the Internet.

Mobile code can also be encapsulated or embedded in other file formats not traditionally associated with executable code. An example of this form of encapsulation is the presence of JavaScript in a PDF.^[1]

Mobile code also refers to code "used for rent", a way of making software packages more affordable. i.e. to use on demand. This is specially relevant to the mobile devices being developed which are cellular phones, PDA's etc etc all in one, even with a projected keyboard. Instead of installing software packages, they can be "leased" and paid for on a per-usage basis.

1. ^ "Acrobat JavaScript Specification". http://www.adobe.com/devnet/acrobat/pdfs/5186AcroJS.pdf. Retrieved 18 November 2009. 

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