Microsoft Update had been working happily on my aging XP desktop for some years. I have trusty desktop set to notify me of updates rather than just zap them in automatically. Now and then I run Microsoft update by hand from Internet Exploder. Today Microsoft Updates started and then choked up with an error message about how it could not access the internet. Hmm. And it popped up a network diagnostic button which I pushed figuring it wouldn't do any harm. Network Diags trundled for a while and then reported that my firewall was blocking ports 80 (http) 443 (https) and 21 (FTP).
So, hit "Settings" and then Microsoft Firewall. And punch a button marked port. And type in the three port numbers (80, 443, and 21). Firewall complained about port 80 claiming it was already present. But it accepted the other two ports. And then Microsoft update started to work.
For all this hacking, Microsoft update did not find any serious updates for me. I browsed the non serious updates and decided than none of them would do my any good.
Still wondering what happened. Did Microsoft tighten up Update so that it needed the HTTPS port? Did some passing virus turn the ports off by way of defending itself? Should I get a better firewall?