search for: dev406mum

Need a scripting help to sort out a list and list all the duplicate lines. My data looks somethings like this host6:dev406mum.dd.mum.test.com:22:11:11:no host7:dev258mum.dd.mum.test.com:36:17:19:no host7:dev258mum.dd.mum.test.com:36:17:19:no host17:dev258mum.dd.mum.test.com:31:17:19:no host12:dev258mum.dd.mum.test.com:41:17:19:no host2:dev258mum.dd.mum.test.com:36:17:19:no host4:dev258mum.dd.mum.test.com:41:17:19:no host4...