Hi - I think not long after this was when my mother board/cpu {one of them} quit on me. system was about 4 yrs old.

so I ended upgrading my system - MB/cpu, ram, sata HD new except for the case and my pc cards. MB had lots of built ons but saved cards just in case.

how old is your system?

We have listings on many free ad/spy/antiv/ in our useful stickys at the top of our threads here.
some miss things that another will catch -same with reg cleaners

I would try a few of each and see if you can fix it that way first.
some AV pgms use more resources that others too.

Is it only the internet that is slowed down or other programs too?