1. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20111 Module 5 Program Security  MModified by :Ahmad Al Ghoul  PPhiladelphia University  FFaculty Of Administrative & Financial Sciences  BBusiness Networking & System Management Department  RRoom Number 32406  EE-mail Address: ahmad4_2_69@hotmail.com

2. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20112 Objectives  Viruses  Types of viruses  How viruses attach  How viruses gain control  Homes of viruses  Virus signature  Source of viruses  Preventing virus infection  Facts and misconceptions about viruses

3. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20113 Program Flaws  Programs behaving unexpectedly  There are no techniques to stop all program flaws –Program controls apply at the level of the individual program and programmer –Software engineering techniques change very rapidly

4. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20114 Kinds of Malicious Code  Virus - A program that can pass malicious code to other non malicious programs by modifying them –Transient - Runs when its attached program executes and terminates when its attached program ends –Resident - Locates itself in memory so that it can remain active even after its attached program ends

5. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20115 Kinds of Malicious Code (continued)  Trojan Horse - A type of program that is often confused with viruses is a 'Trojan horse' program. This is not a virus, but simply a program (often harmful) that pretends to be something else. For example, you might download what you think is a new game; but when you run it, it deletes files on your hard drive. Or the third time you start the game, the program E-mails your saved passwords to another person.  Logic Bomb - A class of malicious code that detonates when a specified condition occurs  Trapdoor - A feature in a program by which someone can access the program other than by the obvious direct call (perhaps with special privileges)

6. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20116 Kinds of Malicious Code (continued)  Worm- A computer WORM is a self-contained program (or set of programs), that is able to spread functional copies of itself or its segments to other computer systems (usually via network connections). Note that unlike viruses, worms do not need to attach themselves to a host program. There are two types of worms--host computer worms and network worms.

7. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20117 COMPUTER VIRUSES IN HISTORY 1972, 1975 Science Fiction 1981, 1982 Apple ][ Viruses 1983 Fred Cohen's experiments at USC 1986 Brain virus 1987 CHRISTMA EXEC Worm (closet case) 1988 Internet Worm 1990 Early Polymorphic Virus - FLIP 1991 Virus Writing Tool - Mutating Engine MtE 1991 370–678 known strands of MS-DOS viruses, over 30 Mac viruses 1992 Michaelangelo: most publicized, little damage overall 1993 Over 2,500 strands of MS-DOS viruses 1995 More companies infecting customers

8. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20118 How Viruses Attach  Appended Viruses - Virus code attaches itself to a program and is activated whenever the program is run. + = Original Program Virus Code Original Program Virus Code

9. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-20119 How Viruses Attach (continued)  Viruses that surround a program - Virus code runs the original program but has control before and after its execution. Original Program Virus Code Original Program Virus Code Part a Virus Code Part b 25060

10. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201110 How Viruses Attach (continued)  Integrated Viruses - Virus program replaces some of its target, integrating itself into the original code of the target. + = Original Program Virus Code Modified Program 25070

11. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201111 How Viruses Attach (continued)  Viruses That Replace a Program - Virus code replaces the target, either mimicking the effect of the target or ignoring the expected effect of the target and performing only the virus effect.

12. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201112 How Viruses gain control (Continued)  Virus changes the pointers in the file table so that V is located instead of T whenever T is accessed though the file system. T File Directory T File Directory T = Target V = Virus T V V Disk Storage

13. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201113 Lance J. Hoffman The George Washington University VIRUS TEMPLATE program virus :="this is a virus" (marker) subroutine infect–executable := {loop: file :=get random–executable–file; if first–line–of–file = "this is a virus" then go to loop; prepend virus to file; } (from Fred Cohen's Ph. D. thesis) subroutine do–damage := {whatever damage you wish to do} subroutine trigger–pulled := {return true if some condition holds (e.g., today = April 1) } replication mission trigger rest of program;} main program := {infect executable; if trigger–pulled then do–damage; goto rest of program;}

14. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201114 Homes for Viruses  Boot Sector Viruses  Memory-Resident Viruses  Other Homes –Application Programs –Libraries

15. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201115 Boot Sector Viruses  boot sector  The portion of a disk reserved for the bootstrap loader (the self-starting portion) of an operating system. The boot sector typically contains a short machine language program that loads the operating system.  An especially appealing place to house a virus –Virus gains control very early in the boot process before most detection tools are active –Operating systems usually make files in the boot area invisible to the user, therefore, virus code is not readily noticed

16. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201116 Boot Sector Viruses (continued)  In an MS-DOS/PC system, the virus may, –attach itself to either of the system files, IO.SYS or MSDOS.SYS –attach itself to any other program loaded because of an entry in CONFIG.SYS or AUTOEXEC.BAT –add an entry to CONFIG.SYS or AUTOEXEC.BAT to cause it to be loaded.

17. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201117 Memory Resident Viruses  Virus attaches itself to memory resident code –Virus is activated many times while the machine is running –Once activated it looks for and infects uninfected carriers

18. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201118 Other Homes for Viruses  Application Programs –Virus macro adds itself to startup directives –Virus embeds itself in data files  Libraries - Desirable home for viruses –Used by many programs –Shared between users –Spreads infections to compilers, linkers, runtime debuggers, etc.

19. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201119 Virus Detection  Virus Signature - The execution and spreading characteristics of a virus have certain telltale patterns  Virus signatures are used by virus scanners to detect the virus –Storage Patterns –Execution Patterns –Transmission Patterns

20. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201120 Storage Patterns  Virus attaches itself to a file and changes its size  Virus obliterates all or part of the underlying program, not affecting its size, but impairing its function

21. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201121 How Virus Scanner detects Storage Patterns  Use a code or checksum to detect changes to a file  Look for suspicious patterns such as a JUMP instruction as the first instruction of a system program

22. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201122 Transmission Patterns  Not confined to a single medium or execution pattern. Example: –Virus arrives on a diskette or from the network –Travels to a hard disk boot sector –Reemerges when computer is next booted –Remains in memory to infect other deskettes

23. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201123 Virus Protection NO REASON NOT TO HAVE VIRUS PROTECTION ALWAYS KEEP YOUR VIRUS DEFINITIONS UPDATED ALWAYS SCAN ON A REGULAR BASIS

24. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201124 Virus & Malicious Code Defense  Detect and prevent distribution: –At the mail gateway –On the mail servers –On the file servers –On the desktops  Plan for perpetual upgrades  Challenges for home and mobile workers –Compliance –Software Distribution –Cable Modem and xDSL

25. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201125 Preventing Virus Infection  Use only commercial software acquired from reliable, well established vendors  Test all new software on an isolated computer  Make a bootable diskette and store it safely  Make and retain backup copies of executable system files  Use virus detectors regularly

26. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201126 Truths and Misconceptions About viruses  Viruses can infect systems other than PCs/MS- DOS/Windows  Viruses can modify hidden or read-only files  Viruses can appear in data files  Viruses spread by ways other than just diskettes  Viruses cannot remain in memory after a complete power off/power on reboot  Viruses cannot infect hardware

27. Network Security Philadelphia UniversitylAhmad Al-Ghoul 2010-201127 QUICKIE VIRUS SAFEGUARD PLAN Limit sharing of software Be ready - have staff prepared Use virus detection software BACKUP YOUR DATA Central security management knows what you have Recalls: 90% may not have removed diskette from box! (So don't panic!)