Unscrupulous Sydney landlords are ripping off foreign students and the less wealthy.

A house has been discovered in the suburb of Ultimo with 58 beds crammed into a three bedroom home.

The City of Sydney is cracking down on so-called slumlords with a new taskforce to tackle the growing problem.

Authorities say the mostly-inner city accommodations are being advertised through social media, with some real estate agents also profiteering.