It was midmorning when the phone rang. The voice on the other end belonged to an American Express representative, who had questions about my credit card usage.

"Did you make a purchase at a Union 76 service station this morning?" he asked.

Nope, I haven't left the house.

"Did you use your American Express card at two service stations yesterday?"

No, I haven't used the card all week.

"Let's go over some other charges and see if there are others you don't recognize."

Identity theft has been around for years, and credit cards are familiar targets. It was only because of three similar purchases in the same locale within 24 hours that credit card supersnoops sensed a crime. But this incident was different from most. My card wasn't missing, and I don't dispose of old statements or receipts in the trash, where the account number could be obtained. So how did someone get my number?

Dublin police Detective Alan Dumatol, who investigates fraud and identify theft, said it likely was stolen by a "skimmer" in a card-reading machine. Card readers are everywhere -- in ATMs, checkout lines, parking meters -- but unattended gasoline pumps are especially inviting targets.

"Skimmers are common," he said. "A few years ago, Antioch PD arrested an organized crime group out of Los Angeles that used them all around the Bay Area."

A criminal opens the pump when no bystanders are around and installs the device. With advances in technology, any information gathered can be transmitted wirelessly and a card counterfeited almost at once. ("You can get the stuff you need on the Internet," Dumatol said.)

Aside from visible tamper marks on the pump, the crime is nearly impossible to detect. That's why it's wise to closely monitor billing statements every month.

Dumatol spends most of his waking hours chasing identity thieves. At this time of year, income tax fraud ranks high on his checklist.

"A scam artist will obtain your Social Security number and file an online return for a refund," he said.

Old-school crooks rifle through carrier boxes, looking for incoming W-2 and 1099 forms -- or outgoing tax returns awaiting pickup. Sometimes scammers will phone victims posing as government officials, asking for tax I.D. numbers.

More commonly, the hook is baited with an innocuous e-mail, designed to look like it came from a bank or a federal agency, seeking personal information. Be forewarned: The IRS never asks for information by email, and your bank doesn't need your Social Security number. It already has that on file.

Another tip from Dumatol: Don't open emails from unknown senders. Clicking the wrong link can unleash malware that will search every document stored on your hard drive.

The crooks in this line of work are real go-getters. According to Reuters, the Treasury Department detected 1.2 million cases of tax identity theft in 2012. So it's not just the government that wants your money. There are scam artists lying in wait.

It makes my experience with the credit card seem like chump change. Still, I'm glad American Express was on the ball.

I don't need criminals robbing me blind at the gas pump. That's what oil companies are for.

Contact Tom Barnidge at tbarnidge@bayareanewsgroup.com.