Virdem

<h2 id="infection-and-symptoms">Infection and symptoms</h2>
<p>Virdem overwrites the host with its own code and saves the original program at the very end. It was a direct-action virus and did not spread fast. It infected only files that had a COM extension.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> When an infected file is run, the next uninfected program becomes infected.
</p><p>When infected, small COM files, less than 11k, grow by 2559 bytes and larger files grow by 1336 bytes. Infected programs ask to guess the user a number between 0 and n such that the number matches the generation number of the virus plus one. A correct guess allows that program to run. Otherwise, it exits.
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<h3>Technical details</h3>
<p>It doesn't intercept interrupt 24h so a write-protected disk gives an "Abort, Retry, Ignore" message. Read-only files are set to read/write, infected and then not set back to read-only. The virus had two <a href="/facts/NOP_(code)/uGcGefyG">NOP</a> instructions at the beginning of the file.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
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<h2 id="external-links">External links</h2>
<ul><li>Malware Example: VIRDEM.COM</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Bhargav, Abhay (2010-09-14). Secure Java: For Web Application Development. CRC Press. ISBN 978-1-4398-2356-9. <a href="978-1-4398-2356-9" target="_blank">978-1-4398-2356-9</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Skoudis, Ed; Zeltser, Lenny (2004). Malware: Fighting Malicious Code. Prentice Hall Professional. ISBN 978-0-13-101405-3. <a href="978-0-13-101405-3" target="_blank">978-0-13-101405-3</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Salomon, David (2010-08-05). Elements of Computer Security. Springer Science & Business Media. ISBN 978-0-85729-006-9. <a href="978-0-85729-006-9" target="_blank">978-0-85729-006-9</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Danesh, Arman; Lau, Felix; Mehrassa, Ali (2002). Safe and Secure: Secure Your Home Network, and Protect Your Privacy Online. Sams Publishing. ISBN 978-0-672-32243-3. <a href="978-0-672-32243-3" target="_blank">978-0-672-32243-3</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Szor, Peter (2005-02-03). The Art of Computer Virus Research and Defense. Pearson Education. ISBN 978-0-672-33390-3. <a href="978-0-672-33390-3" target="_blank">978-0-672-33390-3</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Solomon, Alan (2012-12-06). PC Viruses: Detection, Analysis and Cure. Springer Science & Business Media. ISBN 978-1-4471-1031-6. <a href="978-1-4471-1031-6" target="_blank">978-1-4471-1031-6</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
</ol>

Virdem open-in-new

Virdem