Just found out last night BlackICE Defender DOES keep out them Sub7 trojan. Someone tried to hack me using it, but failed. Tried 6 times in fact. I only has it on cautious setting too, so it was only blocking some unsolicited inbound traffic.
I'd hazard a guess that you were scanned by someone looking for sub7 infected machines, rather than someone trying to hack you using sub7, assuming you aren't infected with the sub7 trojan - the scan would have passed over you firewall or not, the main difference being you are now aware of the scans. The sub7 trojan is not "injected" remotely to your pc, you have to contract it through some other means - a malicious email attachment for example, once infected those scans will yield results for the eager script kiddies, and unless blackice have changed thier security policies recently, your "firewall" won't do anything about it.