That unpatched flaw in Internet Explorer that we told you about earlier in the week? It's already being exploited by hackers who are using hijacked Web servers and compromised Web sites to launch a wave of attacks against Microsoft browser users. The exploited servers and sites are dropping a variant of SDbot, which is a family of backdoors which provide hackers with total access to infected computers. Microsoft says the impact is limited so far. But security experts aren't so sure the attacks won't spread like wildfire.