Covert Channel exploit, plus strange goings on

ESS v4.0.467.0 Firewall module 1051
W7 Ultimate 64bit

Recently I've been suffering from some strange symptons.

Firefox can't resolve PDF downloads,
Windows 7 loses internet connection if left idle
PocMail receives images, pdf's and document attachements corrupted.

This has been occurring for the past week or so.

I have tried disabling the firewall and that appears to solve the email attachment problem.

The W7 and Firefox problem, might be due to a W7 update or the fact I've updated my NVidia driver, however, I don't have this problem on my laptop, which is running v4.0.437 and is connected to the same router via UTP and WiFi

I've just checked in my firewall log and it is reporting that it has detected 'Covert hcannel exploit in ICMP packet' the source being my computer IP address and the target appears to be Google and Microsoft!

I note it also reports a port scanning attack when two W7's notice they are on the same network - this is of course due to W7's new autoscanning for HomeGroup - which I don't have set up.

Are these likely to be a firewall problem, or have I perhaps been 'infiltrated' ?