Um, I didn't read the link, my computer is slow and so I am reluctant to open new windows, however, I just wanted to say, I get those often as well, not ACK, I get SYN attacks, but they're both DoS attacks. Nothing to worry about, and you could report these to the ISP, which you could probably find out with some network lookup tool or neotrace. It won't hurt you, and even if you didn't have a firewall, it wouldn't have done anything unless you had a port that was accepting connections. It might be a good idea to read up on TCP/IP if you're interested in what this person was trying to do. Basically, don't sweat it, its just that you're logging these things now, chances are people were trying to attack a range of computers, that you were in, and this had probably been going on long before you had a firewall.