McAfee's VirusScan Plus 2010 (Personal Firewall 11) is seriously broken

After two days of trying to find the root cause of a degraded write speed to both my NAS servers, I think I found the source of the problem. It's the new McAfee VirusScan Plus 2010 edition I installed.

Before with the old version: 30-50 MB/s

With the new version 100-200 KB/s

I tried to open the usual ports (445, 137-139 etc) but no effect on the speed whatsoever.

Only after deinstalling McAfee things are back to normal again.

A bit more research is needed, because since this week McAfee forces you to upgrade to the latest version.