Think of it as one more reason not to write checks.

Hackers believed to be operating out of Russia have figured out a high-tech way to carry out the decidedly low-tech crime of check fraud, a computer security company says — writing at least $9 million in fakes against more than 1,200 legitimate accounts.

But these hackers got the account information in an unusual way: They broke into three websites that specialize in a little-known type of business — archiving check images online.

Check counterfeiting is a crime that savvy Internet criminals usually pass up. After all, it's far easier for them to make money by stealing credit cards and online banking passwords.

The scam was discovered by SecureWorks Inc., an Atlanta computer security company. The organization says it is working with the FBI and says the hackers have not been caught.

Retailers and other businesses use the sites to store records of all the checks they write. Check-cashing operations use them to sock away images of checks they receive. And some banks pay them to store images of customers' checks, so the customers can see them when they log in to their online banking accounts.

The criminals downloaded all the images they could find, grabbing bank routing numbers, names and addresses and even signatures of legitimate account holders. They used the information to create their own checks using easy-to-acquire software and printers.

Because all the account information is real and the victims don't know their accounts have been compromised, the odds of the checks going through are high.

SecureWorks notified the three sites and said they have closed their security holes, but warned that the scam is ongoing and targeting other, similar sites.

"It's not the standard kind of criminal operation," Joe Stewart, director of malware research for SecureWorks' Counter Threat Unit, told The Associated Press ahead of the report's scheduled release Wednesday.

"Check counterfeiting is kind of old school, but these guys have figured out how to make it highly automated," he said. "They can get all this data and use that to write counterfeit checks all day long."

The research was being released in conjunction with the Black Hat computer security conference in Las Vegas, which runs Wednesday and Thursday and draws security professionals from around the world to hear about the latest vulnerabilities and attacks and ways to thwart criminals.

Notable presentations this year are to include a demonstration of how to break into widely used ATMs, a talk that was pulled last year by the researcher's employer after complaints from the ATM maker. Researchers are also expected to discuss vulnerabilities in smart phones and in the technology used to secure online transactions.

A consistent theme at Black Hat, and at the related DefCon conference this weekend in Las Vegas, is that most Internet criminals are now motivated by money rather than mayhem. And they're getting more clever in their approaches as banks and other valuable targets tighten their security, as SecureWorks' three-month investigation into the check-counterfeiting ring found.

Dan Clements, a computer security expert who wasn't involved in SecureWorks' research, said the scheme represents a "very significant" escalation of the abilities of online crooks.

He said people should watch for small test charges that criminals make to figure out which accounts are still active, and avoid writing their driver's license numbers and other personal details on checks. He said the attackers were shrewd in their choice of targets.

"I think it's brilliant — it's where the data is," he said. "It's a way to get into these accounts and they don't need to be in the country."

It's unclear how much of the $9 million in that scam the criminals actually got to keep.

The main bottleneck lies with the "money mules" — people recruited from online job sites to launder the money.

They were sent the bogus checks — via overnight shipping paid for with stolen credit cards — and asked to deposit them into their own bank accounts. They were then supposed to wire a portion to accounts in Russia.

Stewart said the six "mules" he was able to reach all told him they hadn't wired any money to the criminals because either they or their banks got suspicious. Many more likely did wire the money, however.

Stewart uncovered the scam while investigating malicious software that steals banking passwords.

In eavesdropping on one criminal group's communications, which he was able to do by infecting his own computer with the malicious program the group was using, he noticed that they were doing something unexpected: collecting massive amounts of images of checks.

He found a file logging all of their transactions, which revealed that 3,285 checks were written against 1,280 accounts since June 2009. Most checks were written for less than $3,000 to evade banks' anti-fraud measures. Overall, he saw about 200,000 stolen check images — suggesting the criminals have only exploited a fraction of the accounts on which they have information.

SecureWorks isn't identifying the hacked sites.