Well, Google reveals quite a
few hits on
evd000.encBlackICE is simply logging the network traffic (or rather the blocked intrusions) into these log files (evdXXX.enc). Since the log files contain the intrusion code (such as SQLSlammer in this case), avast! detects the corresponding virus in the log as well.
In addition to (the usual) note that it's rather stupid to log this kind of stuff in plaintext (= unencrypted) to disk, I can only suggest either to turn off this BlackICE feature (sorry, I'm not familiar with BlackICE), or put the correspoding mask into the list of avast! exclusions (both On-demand in program Settings, and On-access in Standard Shield settings).