4.2.2.2 is the IP address of a DNS server owned by the company Level 3 Communications.
Network users primarily use this address to check their connectivity to the internet by pinging this address.
Because the address of this DNS server is easy to remember, its use is spreading rapidly among IT and ICT professionals who quickly want to check the connectivity of a device.(For an example, see this handout from the Bill & Melinda Gates Foundation)
It is also popular with Information technology and ISP help desk personnel, who find the IP address simple to tell people over the phone. It is often more convenient for them to instruct someone to ping 4.2.2.2 rather than the ISP's own DNS server in order to test connectivity.
The Bobin.A Windows virus pings this address to detect an active Internet connection on an infected machine.[1]
4.2.2.1 through 4.2.2.6 are all valid Level 3 DNS servers. credit to . Manuelvde and Dina and a few other minor contribs. You can find one useful article on this DNS address here http://itechtrick.com/2013/12/DNS-4.2.2.2.html .