How was my DNS record tampered on the resolver of ISP???

[Bill Manning]

 Well, It appears that the domain you specified:
	mydomain.com
 is properly delegated to the following servers:

	;; AUTHORITY SECTION:
mydomain.com.           3D IN NS        ns1.mydomain.com.
mydomain.com.           3D IN NS        ns2.mydomain.com.
mydomain.com.           3D IN NS        ns3.mydomain.com.
mydomain.com.           3D IN NS        ns4.mydomain.com.
....

and www.mydomain.com resolves to:

$ dig www.mydomain.com

; <<>> DiG 8.2 <<>> www.mydomain.com 
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 0
;; QUERY SECTION:
;;      www.mydomain.com, type = A, class = IN

;; ANSWER SECTION:
www.mydomain.com.       1D IN A         64.75.34.137

....