You weren't hacked. Port 80 is HTTP, which is the normal webserver port (just like http:// on the front of URLs). Someone was probably following an outdated IP or a bad DNS record on their ISP's nameserver and their browser was trying to contact your machine on the HTTP (hypertext transfer protocol) port. You will probably get requests on 21 (ftp), 23 (news), 25 (smtp), 80 (http), 109 (pop), 110 (imap) regularly. If you see probes on those ports, dont worry about it.