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Logs tell you important messages about what is going on with your machine. If you know what is happening then you are more likely to know when an attack is happening. This helps you prevent anything bad. The logs are found in the /var/log/ directory. The logs that are probably the best to look at would be the /var/log/messages file and the /var/log/secure file. You can look at it by typing:
bash$ less /var/log/messages
Get familiar with the logs and know basically what to expect. If something looks strange then that might be an attackers sign.