Operating System and Computer Security What does Operating System do

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Operating System and Computer Security

What does Operating System do

  • Manages all the resource in a computer (including processor, memory, i/o devices)

  • Provides an interface between the hardware and application software.

Mostly used OS

  • Desktop

  • Windows

  • Mac OS

  • Unix/Linux and their siblings.

  • PDA

  • Palm

  • Pocket PC

  • Embedded Linux OS

Macintosh Operating System

  • Evolved from 1984’s original MacOS

  • 1984 Mac was first commercial computer with Graphical User Interface (GUI) and mouse

  • Currently MacOS 9, MacOS X

  • Inventor of trash can, alias (shortcut), pull-down menus, etc.

Mac OS Details

  • Control Strip

  • Alias (same as shortcut)

  • Single-button Mouse (can be customized)

  • Sherlock 2 (global search utility, copied in Windows 2000 and Windows ME)

  • Easy to use, hard to troubleshoot

Windows OS

  • Windows is built on top of MS-DOS, the MicroSoft-Disk-Operating-System, based QDOS.

  • Windows 1.0 very delayed, very poor quality

  • Windows 3.1 (c. 1992) first usable version, still very limited in comparison to MacOS 6

  • Windows 95 revolutionary for Intel based computers, but, just a copy of Mac OS

Windows 95

  • Stole Recycle Bin, Shortcuts, and Menu System from Macintosh OS

  • Excellent user-friendliness for operations

  • Like MacOS, suffers from un-friendliness for troubleshooting

  • Excellent multi-tasking capabilities (run multiple programs)-uses virtual memory


  • The ability to run several programs at the same time.

  • CPU can only run one program at a time. OS will switch programs for it. Since the switching is so fast, it looks like running multiple programs at the same time.

  • Two multi-task mechanism

  • Cooperative multi-tasking (program voluntarily release CPU )

  • Preemptive multi-tasking.(OS deprives the CPU control when time is up)

Windows History

  • Windows 95 for home machines, stable, simple

  • Windows NT 4.0 for business/office computers

  • Windows 98 replaces 95, very unstable, just a facelift

  • W98 Release 2 much better, still sucked

  • Windows 2000 replaces Win NT 4.0

  • Incredibly stable, not very backwards compatible

  • Windows ME (Millennium Edition) replaced W98 (fall 2000)

  • Almost no new features

  • Seems a little more stable than W98

  • Faster Startup

Windows XP

  • Released last year

  • Home version and business version based on same OS

  • Previously, Win NT & 95 different, 2000 and ME different

  • More stable than Win 98/ME, not as stable as W2000

Linux and Unix

  • Unix was the first usable OS and still widely used today. It runs on special computers, e.g. Sun, Silicon Graphics, HP, DEC

  • Linux was a miracle, initalized by Linus Torvalds and maintained by programmers all over the world.

  • Both are based on a stable command line OS

  • By comparison, Windows based on unstable command line OS, MS-DOS

  • Both Linux and Unix use an X-Windows GUI

Ranking the Operating Systems

  • Unix

  • Linux

  • Mac OS X

  • Windows 2000

  • Mac OS 9

  • Windows NT

  • DOS

  • Windows 95

  • Windows ME

  • Windows 98

  • Mac OS 9

  • Windows ME/98/95

  • Mac OS X

  • Windows 2000/NT

  • Linux

  • Unix

  • DOS!

Future of Operating Systems

  • Microsoft must address stability problems in home computers – Windows XP was a small step

  • Linux becomes more popular, but only for advanced users and in server market.

  • Macintosh’s market penetration more based on hardware appeal rather than software

  • In old days, Macs succeeded because they were the only GUI on the block. People bought Macs for the software

  • Windows is such a good copy that hardware, reliability, and price is now a big reason for the purchase of a Macintosh

Computer security challenges

  • Virus

  • Email Virus

  • Worm

  • Trojan Horse

  • Spam


  • Viruses are fragments of computer code that can piggyback on the normal programs

  • When normal program is infected by virus, virus will run first every time you start the program.

  • Viruses can duplicate themselves and infect other programs.

  • Original virus are less and less popular now.

  • People don’t copy files from others, but would rather download from the original source.

  • Anti-virus software is widely used.

Email virus

  • An e-mail virus moves around in e-mail messages, and usually replicates itself by automatically mailing itself to dozens of people in the victim's e-mail address book.

  • Two kinds

  • Executable attachment (.exe .vbs .com .bat files).

  • Macro language viruses.

Fact about email virus

  • BOTTOM LINE :There is *NO* such thing as an E-mail text virus!

  • You can not get a virus or any system damaging software by reading an e-mail*. E-mails (that is, the ACTUAL message can not contain viruses)

  • Email viruses always resides in the attachment. So don’t run any suspect attachment files.


  • A worm is a computer program that has the ability to copy itself from machine to machine by taking advantage of the security hole in the system.

  • Security holes are bugs in the OS.

  • This is the most serious threat now

  • Your Computer can be infected by just plugging in the internet.

  • MSblast and SoBig are the recent worms that damage hundreds of thousand computers.

Trojan Horse (back door)

  • A Trojan horse is simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk).

  • Trojan horse usually does replicate itself.

Suggestions to secure your computer

  • Use anti-virus software.

  • Update your computer regularly.

  • Be careful with the email attachments

  • Safe: .jpg .bmp .pdf .txt ….

  • Unsafe: .exe .doc .xls .ppt …

  • Avoid email software by Microsoft (outlook, outlook express…). They are mostly targeted.

  • Use firewall or router to protect you from worm attack.

Spam (junk mail)

  • Spamming is business

  • Most effective way to stop it is legislation. Most states passed law to restrict it, but none fully banned it.

  • How spammers get your mail.

  • Web search

  • Sending test emails

  • Exchange or buy from other spammers

  • A case study: How an can HTML email reveal your identity.

Suggestions to fight spam

  • Never reply junk emails

  • Moreover, never even open them.

  • Don’t post your actual email address in the website.

  • Sparty_at_msu.edu

  • Sparty@NOSPAMMINGmsu.edu

  • Use a picture of your email address.

  • When send group emails, put all the recipients in the BCC field to protect other people.

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Operating System and Computer Security What does Operating System do

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