How long do you keep your logs for? The answer can vary wildly depending on the industry you work for. As an example, most VPN providers specifically note that they do not hold logs, so even if a government requested certain logs, they would not have them. The logs they don’t keep are likely to be only user access logs. They’ll still have internal system logs.
Ultimately keeping logs for long is of little benefit unless there is a security reason to do so. The recent shellshock bug is a great example of when older logs can be useful. You may have a honeypot out in the wild and once a known issue comes to the fore, scan your logs to see if this particular bug has been exploited before it was well known.
Country and industry regulations will also influence the amount of times logs are kept. Many countries require that documentation and logging data be kept for a certain amount of years for any number of reasons.
I’m interested to know how long you keep logs for. What particular logs as well as why that length of time was chosen.