Linux Maintenance

I have recently installed the most recent version of Ubuntu and am in
the process of totally switching from Windows XP. I have been a
computer user for many years and have tried Linux in the past but this
is the first distro I have actually installed and got working
correctly. My question is about maintaining Linux. I have automatic
update enabled and have installed ClamAV and run a full system scan on
a weekly basis. Do I have to worry about Spyware etc and do I have to
run a Chkdsk tool and defragmenter on the hard drive to keep things
running smoothly. Thanks in advance for any replies.

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