Age Concern chief executive Ann Martin said she was disgusted and disturbed by the attacks. Older people were often seen as soft targets by offenders.
Mr Groombridge said knowing who was at the door was crucial to keeping safe.
"Most of [the elderly] are shut in and the only way [to identify who's calling] would be to check at the door," he said.
"Some of them have spire holes cut in the door so they can see who the person is, but that's not universal."
Wairarapa had experienced cases of people coming to the door to take advantage of old people, Mr Groombridge said.
Early last year, fears for elderly residents were high when a child gang in Featherston began preying on elderly people.
A stream of petty crime saw dozens of incidents where homes, sheds and property were ransacked and items, including alcohol, stolen.
Gang members targeted elderly people, badgering them for money, sparking fears someone would be attacked or hurt.
Speaking generally about cases involving elderly victims, Dr Trevor Bradley, a lecturer in criminology at Victoria University, said they were usually targeted by opportunistic criminals in search of financial reward.
"Elderly people are interpreted as particularly vulnerable. There is also an expectation that older people may have built up a large volume of assets, whether they be jewellery, cash or whatever."
However, when attacks occurred in less affluent areas, it suggested offenders were not just motivated by financial reward, but might just enjoy "hurting people".
Mr Bradley said people who committed such crimes tended to lack empathy, and their behaviour would often reflect their own personal circumstances.
The callousness of crimes against elderly victims was often recognised in court.
"When offenders victimise particularly vulnerable people, children, the elderly - then they tend to get more serious punishments."
Napier police crime prevention officer Paul Miller said offenders were often young and would take advantage of being invited into an old person's home.
They would con themselves through the door by arriving on a pretext like fundraising, or conducting a survey.
"Old people living alone are quite vulnerable and tend to be quite trusting and the message constantly is they should be careful about who they let into their home." APNZ
Tips for staying safe
Don't open the door unless confident who it is, and ask for identification
Take extra care during summer if spending time out the back of the house
If taking a shower or going for a nap, secure the house as if you were out
Don't put too much trust in screen doors, they are lightly constructed and not to be treated as security doors
