Unknown cause for redirect on 80 port

I have an Ubuntu 14.04 server with Apache 2.4.7 running there, hosting one site on 80 port. Today I discovered that every request to 80 port redirects to another website with response:

HTTP/1.1 301 Moved Permanently
Server: nginx/1.6.2
Date: Thu, 15 Jan 2015 13:37:18 GMT
Content-Type: text/html
Content-Length: 184
Connection: keep-alive
Location: some.website.com

I don't have nginx installed, bit still searched for a nginx process with ps ax | grep nginx command with one result: 25759 pts/1 S+ 0:00 grep --color=auto nginx. It didn't seem like the offending process but still: kill 25759 yielded -bash: kill: (25759) - No such process

Next, I stopped apache (it changed nothing about redirects), and decided to see, who listens to 80 port with the command lsof -i :80 | grep LISTEN which told me nothing, and if I list all listeners with the command: lsof -i | grep LISTEN I get the following list:

sshd        673     root    3u  IPv4   7078      0t0  TCP *:ssh (LISTEN)
tinyproxy   972     root    0u  IPv4   7654      0t0  TCP *:9582 (LISTEN)
Xtightvnc  1173     root    0u  IPv4   7914      0t0  TCP *:x11-1 (LISTEN)

All of which are known entities. If I start apache the following line is also there:

apache2   25926     root    4u  IPv6 139312      0t0  TCP *:http (LISTEN)

Next I thought about iptables, but iptables -L shows empty list:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

So, the question is how do I find what causes this redirect (checked from several different computers with different internet providers) and remove it?