Protecting Instant Messenger File Transfers?

Does anyone know which Grisoft .exe program one should choose when protecting Instant Messenger MSN and Yahoo?

It gave me the selection in the attachment, but hovering over them or even running them, didn't give me any clues.

UMMM Ya Norton antivirus
I wouldnt use AVG on a bet.
I have cleaned way too many viruses off avg protected machines

Yes, but, my Norton runs out in a few days and my PC is due a re-format, so I wasn't prepared to pay the subscription only to lose it when Ellie and I are able to get round to reformatting my PC.

My ISP does have basic anti-virus software on their email servers, although I'm aware viruses can come in through other routes.

Grisoft was the only FREE alternative that had been recommended to me, so ..... ??

1: Norton allows a few reinstalls without looseing anything
2: Antivir is likely a better choice by far.

Oh thanks Ferrit, I didn't realise it allowed a few reinstalls, but too late, it's gone.

Just tried running these checks from the Symantic site
Symantec Site checks

The Firewall test ran beautifully (I've got free Zone Alarm on at the mo.) and it said my PC is well protected, but the Virus check didn't even manage to install the checking program, so I think there's something wrong with that?

I much prefer Norton, but gonna have to wait, I think ...