Sorry for the late reply. I wasn't able to register an account back when mikacctv first asked the question and for some reason it worked this time
This is almost certainly what's known as "BrickerBot" attempting to disconnect a hacked/insecure camera from the Internet. Are you able to retrieve the user database by requesting http:///cgi-bin/user/Config.cgi?/nobody&action=get&category=Account.* ? If so then anyone on the Internet can get admin access to it and it'll end up being targeted by malware such as Imeij.
I recommend securing the camera behind a VPN or even just to limit access to it by a firewall. Simply changing the port is not a long-term fix. Avtech may also be able to offer a firmware upgrade which fixes the vulnerability (but they've been slow/unhelpful so far).