If you want to know about the specifics of a DCOM exploit, Google can turn up info. If there is a pending fix, you'd find it in Windows Update (or at worst, on microsoft.com if it hasn't been pushed out on WU), which should be run on a regular basis. Just relying on manually patching specific exploits whenever Avast randomly detects them is an insufficient security protocol.
This is a firewall issue. The purpose of a firewall is to block unsolicited connections, in or out (such as random worm probes). You should install a full-fledged firewall to block such worms before Avast's shield can even see them (XP's firewall is useless). If you have a firewall and such probes are getting past it and detected by Avast, you need to either fix the settings or get a better one. I hear Komodo makes a good free one. This article should be of use:
http://arstechnica.com/guides/tweaks...sx-windows.ars
You really should invest in a router, though. No amount of software can possibly replace a SPI firewall/router box (even just a wimpy NAT router helps) in terms of random probe protection. Dropping all unsolicited incoming connections before they can even reach the PC is the best protection; on-system AV and firewalls are the last line of defense. You can probably pick up a cheap used router for ~$20.