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jan19 - CS 426 class...

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CS 426 class Jan 19, 2012 www.cs.purdue.edu/homes/ssw/cs426/{index.html,syll.pdf,outline} (General purpose) Program security These ideas apply also to OS and DB. Read Chapter 3 How does a virus attach? 1. at beginning of pgm, so it can run before the pgm; or 2. at beginning and end of pgm, so it can run before the pgm and cleanup 3. in many places in the pgm; writer must understand the pgm 4. to email, say, in graphic, document or image attachments How does a virus gain control? Pretend to be a useful pgm and 1. change a pointer; or 2. change part of the OS Some viruses, such as those in email, execute only once. Other execute repeatedly and hide in 1. boot sector, inserted in a chain of sectors 2. parts of the OS that stay in memory (resident viruses) 3. apps with macro features, like word processor 4. libraries Viruses may be detected by their signatures: 1. storage pattern - its code on a disk or in memory 2. execution pattern - modify files, may seem normal 3. transmission pattern - disk, network, email. Virus scanner can find some viruses by looking for their signature Polymorphic viruses change their signatures continually by 1. moving around pieces of their data and code
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