Free Anti Spam Software

1) My PC came with Webroot and Norton installed (about a year ago and it’s time to renew). Is there an advantage to buying the software vs downloading it? Would/Will I still have to renew again after a year if I went and bought it?

2) When comparing what you get for free vs. what you pay for, does having a firewall mean you have all the Anti stuff (Virus, Spam, Spy-Ware) by default and what really is the distinction?

I keep getting this pop up window without even opening my browser… it shows as

VirusRemover2008
Online protection against malicious software

It looks like one of those where they try to trick you into signing up for some anti virus you dont even need, how can I get rid of this ? has anyone ever had this problem before ? I dont have an anti virus currently so I know this could be an issue but i can also tell the difference between a legit offer and a spam pop up and I know thats what this is….

I have McAfee but it’s so expensive, I’d rather find something cheaper. I’m scared to just go download an anti-virus program though because of malware programs - the programs that look authentic but then either spam or virus you. Does anyone know a safe, authentic program? Anti-hacking software would be appreciated, too.

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I have McAfee Total Protection installed and it does not find anything. I also have run Microsoft Malicious Software too, with nothing found. I still keep getting these popups that are just ads. WHY?!?
Additionally:
My firewall is enabled.
McAfee Total Protection is supposed to cover spyware, adware, malware, etc. It’s as 12-in-1 product.
I ran adaware prior to purchasing McAfee and it found nothing.
Spykiller also found nothing.
My pop-up blocker is also enabled.

I hear arguments about Norton and other programs, and I’m not sure which to buy now.

Free is preferred but paid is okay.

I already know of AVG and Norton isn’t good. Anything else I’m missing?

thank for your help

Please suggest me which one is better among these -
1. NOD32 Anti-virus v3,
2. ESET Smart Security v3,
3. Kaspersky (latest version),
4. Trend Micro (latest version),
5. BitDefender Total Security 2009.