Some local police are reporting an increase in credit and debit card fraud cases this year, with thieves using high-tech tools to steal confidential financial data from unwary customers at stores, restaurants and gasoline stations.

The number of cases has "really exploded in the last month and a half," said Jim Graham, a detective with the Thousand Oaks Police Department.

"There's been a big jump in this from Bakersfield all the way down the coast of Southern California," he said.

Many of the thefts are reported to banks but not police, so exact counts of victims and dollar losses are hard to come by, he said. Authorities estimate worldwide losses to be in the billions of dollars annually.

Thieves have an array of devices to pilfer credit and debit card numbers, including "sniffer" software programs that capture PINs and other sensitive information.

One of the more popular devices being used in Ventura County is a "skimmer," Graham said. The gadget captures information on a card's magnetic strip, which then is cloned to withdraw money out of a person's account at an ATM or to buy merchandise.

Skimming machines were once bigger, but thieves are now making "some the size of a matchbox," Graham said. That makes it easier for thieves to place them on pumps at gasoline stations or at store terminals where shoppers swipe their cards.

Police say thieves return a week or so later to retrieve the skimmers and extract the data inside.

"If you figure they're getting $300 to $400 for every card, it's not hard to see how profitable it can be," Graham said.

It's also a hard-to-solve crime, said Rick Kline, an Oxnard police detective who investigates fraud. "We're solving maybe five out of 100," said Kline.

While many stores, ATMs and gas stations have video surveillance cameras, "the quality of the videos is often very poor," Kline said. Also, thieves "generally wear a hat" or other disguise, "making it very hard to identify them," he said.

"Most of these crimes are solved when the victim has an idea of who's behind it," Kline said.

Susan Nettles of Ojai has yet to find out who stole her debit card information and then used it three times at ATMs in Huntington Beach to withdraw almost $600 from her account, although she thinks she knows where her card was compromised.

"I think it happened at the Cost Plus store in Oxnard," Nettles said.

Cost Plus announced in July that the electronic PIN pads at eight of its Southern California stores, including the one in Oxnard, might have been tampered with between February and April. Since then, Cost Plus has made numerous changes to improve security, including replacing some of the PIN pad machines, said spokesman Dan Gagnier.

"The newer machines are a lot harder to tamper with," Gagnier said. The company "wants its customers to feel comfortable using their cards at our stores."

Cost Plus also is working closely with credit card companies, banks and law enforcement agencies "to ensure that any of its customers affected by this incident are identified."

Nettles filed a police report, something authorities say many victims fail to do. She said she now is leery of using her debit card. "Now I try to use cash when I can," she said.

Thieves aren't the only ones availing themselves of high-tech tools. Credit card companies and banks are increasingly relying on sophisticated software to monitor customer spending habits. The software flags out-of-the-ordinary purchases or payments and alerts authorities.

Robert Meyers, a Ventura County supervising deputy district attorney who investigates fraud, said such software has "generated many more cases" for prosecutors.

But investigators said victims also should report the crimes to police. For starters, it would give investigators a better idea of the scope of the problem, Graham said.

"We're able to see if there are patterns," he said, including whether a sizable number of victims might have purchased things at particular stores or places.

Consumers also should monitor bank and credit card statements. Kline knows of victims who had not inspected their statements in months. And they should not throw documents containing sensitive data into the garbage.

"Use a paper shredder," Kline said, "and never pay your bills by sticking them in an unsecured mailbox or clipping them to the mail drop in your front door."