Vulnerable victims, including families and the elderly, have been left shaken after bricks were thrown through the windows of their homes in Burnley.
Police are now appealing for witnesses to come forward following the criminal damage in Cleaver Street during the past week.
Patrols of uniformed and plain clothed officers have now been stepped up in the area following the attacks which took place during the hours of darkness.
A police spokesman said: "The offenders have been throwing bricks through windows of houses during the hours of darkness causing great distress to vulnerable occupiers including families and elderly residents.
"These attacks appear to be random acts of criminal damage and as a response to this we have increased both uniformed and plain clothes officers in the area."
Anyone with any information is asked to contact the Bank Hall Neighbourhood Policing Team PC 269 Kerry Moorcroft, PC 6402 Weronika Strug and PCSO Olivia Hall on 101 quoting reference number EF1711784 , email email@example.com or call crime stoppers anonymously on 0800 555 111.