For the most part, the "attacks" probably aren't serious, but don't take chances. Keep the firewall up. In the last 3 hours, my firewall has detected a large number of "attacks." but it classifies them according to severity. Most of the "attacks" are just port probes (UDP, HTTP, and TCP). None of them raised any serious flags, and were simply blocked and ignored. But I definitely take comfort in the fact that it blocks them, because there are simply too many undisciplined kids out there getting a copy of some trojan and becoming k3w7 h4X0rZ.