There were almost 70,000 cases of it last year, up almost 26 per cent from 2015's figure.

That crime is "theft from a motor vehicle", and car theft experts say it is hard to guard against because a vehicle's defences are only ever as strong as an easily-shattered pane of glass.  

National Motor Vehicle Theft Reduction Council executive director Ray Carroll's advice is simple: "Don't leave anything in your car."

"Thieves will smash the window and steal whatever they can see in the console," he said. "It's not just valuables they take, it's anything.

"People assume that just because the door is locked the car is safe, but any car is only as strong as a pane of glass. They can purchase hammers that shatter the glass really easily and don't make much noise.

"And it costs about $300 to repair the window, which isn't worth claiming on insurance if the excess is $600."

Victoria Police Assistant Commissioner Robert Hill said about one-third of thefts from motor vehicles did not show any signs of forced entry, indicating owners had more than likely left their vehicles unlocked. 

Shopping centres and railway station car parks were common locations for car break-ins, especially as it related to number plate thefts, he said. He said most thefts from motor vehicles involving personal items occurred in residential locations, and tradesmen were commonly reporting tools missing from work vehicles they had parked outside their homes. 

The overwhelming majority of those charged for such thefts were repeat offenders and known to police, he said, and they were stealing items to fuel drug habits or to commit other crimes.  

But Assistant Commissioner Hill said improved investigative practices, forensic techniques and increased resources for tackling thefts from cars were having an impact. 

"While the 2016 data is certainly a concern, our intelligence indicates that there has been a steady decline in the reported thefts from motor vehicles since July last year," he said. 

Even those who work at Victoria Police are not immune from having their cars broken into.

On Wednesday morning, police media officer Creina O'Grady​ found her car had been targeted.

She had parked her Mitsubishi at Melton Railway Station's car park, and had returned from her night shift to find the driver's side window smashed and the steering wheel missing.

She informed the station's staff, only to find more items had been stolen from her vehicle than she had initially noticed.

"I told the guy my window had been smashed and [the thieves] took my steering wheel," Ms O'Grady said. "He replied: 'They took your wheels'."

"I thought he must be hard of hearing because I was saying my 'steering wheel'," she said.

As it turned out all four tyres had been taken and the car was sitting on its axle:

"I thought it was sitting a bit low," she said.

In the postcode of Melton alone, there were 489 cars broken into last year, or about nine per week.

Using the interactive map below, you can see how many thefts from motor vehicles were recorded in your area last year.

Hover over a postcode to see the number of cases last year. If you are using a mobile or tablet device, tap your area to see a breakdown of reports over the past five years.  

As you can see, postcodes in Melbourne's outer suburbs recorded some of the largest numbers of cars broken into.

There were more than 1000 theft from motor vehicle offences in Dandenong/Bangholme, Werribee/Derrimut and Cranbourne/Skye.

In some postcodes in Melbourne's north, the number of cars broken into soared last year. In Craigieburn/Donnybrook there were 940 cases, up from 629 in 2015. Areas incorporating Bundoora, Kingsbury and Coburg also recorded a surge in thefts.

And in regional population centres such as Wangaratta and Moe, the number of cars broken into more than doubled.

Even the state's most crime-free postcode has seen an increase in break-ins. Warrandyte, in Melbourne's south-east, recorded 44 thefts from cars last year, up from 19 in 2015.

But one of the main items stolen from cars are found on the outside of the vehicle – the number plates.

When the most recent crime statistics were published a fortnight ago, Victoria Police Deputy Commissioner Andrew Crisp said 21,000 of the 69,000 cases last year involved number plate theft.

Mr Carroll said thieves were using stolen number plates to drive around undetected in unregistered vehicles, to dodge toll road fines and speed cameras, and to carry out petrol drive-offs. 

Assistant Commissioner Hill said one-way or anti-theft number plate screws had not had the desired impact on reducing number plate theft, and police were working with VicRoads, the Department of Justice and the National Motor Vehicle Theft Reduction Council on ways to improve vehicle identification technology. 

Theft from a motor vehicle has been the most commonly-reported crime in Victoria since 2014. 

Other common crimes last year included non-aggravated burglary (50,503), criminal damage (40,160), breaching family violence intervention orders (38,041) and motor vehicle theft (23,967).