Find out if slow internet access is due to being attacked

Internet access from an ADSL router gets very slow at times. I know there may be many networking reasons for this but let's focus on the security aspect for now: might it be that I am being attacked at the public IP? How can one find out if an attack is going on?

 

Check your router logs, and make sure all the security are in place (password, wifi encryption, etc.)

 

You should review your router's configuration, such as ports and firewall rules (if included) to check for any problem areas that might cause issues.

What time of the day does this occur? 6 pm to 2 am every day?
Check the computers connected to the router for malware. Spambots can degrade your internet connection.
Are you using a router that has wifi included?
If yes check to see if you have any free loaders piggy backing on your network, hogging your bandwidth with their malware infested systems.

Finally, if its a router you could try and telnet into it and get a shell.
This will let you poke around under the hood. While there check out the "flash layout" to see if anything has been uploaded, like a new rom. rom's are very rarely if ever updated, so any changes there would be suspect.