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For an average user (doing on-line payments, etc.), would it be useful to periodically conduct a OS re-installation of his computer to improve security? How often would that be and how much extra security would that be?

Obviously, if you have the almost same system as before (thus almost the same flaws), then you are as likely to be infected the same way you were before OS re-installation. But you could hope to be clean for a moment. Is this improvement relevant? I guess this question is hard since it would be hard (impossible) to assess an average time a system is compromised. Are there any best practices concerning periodic fresh OS installations ?

Would periodic OS re-installation be useful in a company environment?

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I personally would not attach any security to periodically re-installing my operating system, as it would also leave a window of out of date software when you just re-installed your operating system.

There are other ways to limit the chance of infection:

  • correct mindset (don't just click everywhere)
  • up to date operating system and software
  • anti-virus and firewall
  • Host based intrusion detection system (not widely deployed though, but can be a plus)

And in the event you do get infected, then you need to make sure you can roll back to the latest uninfected backup and patch the hole which made infection possible in the first place.

Would periodic OS re-installation be useful in a company environment?

No not a chance, you don't want to start from scratch. What you can do is have have a clean image containing all your software and which is up to date. This is common practice in companies and is called a golden image or golden build.

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Thank you. What is a common interval to periodically deploy golden image? I assume each time an update is available. Besides, are there significant improvements to perform these deployments even if you did not detect any infection (stealthy attacks, 0 day attacks) or is this unnecessary? –  someone Jul 24 '13 at 7:56
    
Actually only on each reinstall, it's kept up to date and used in the event someone needs a computer repaired or rebuild. For instance when you need to restore from backup, you generally reinstall a golden image and then put all files contained within your backup :) –  Lucas Kauffman Jul 24 '13 at 7:58
    
So no measure are usually taken against the attacks we did not detect/suspect. Such paranoid policy is never enforced in practice? –  someone Jul 24 '13 at 8:04
    
If it's employed than there are no files kept...ever. If employed it's done by removing and restoring a complete build after every session. This is for most offices highly unworkable though. –  Lucas Kauffman Jul 24 '13 at 8:05

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