When fraud happens, consumers complain constantly — to their banks, to their friends, and to anyone on the Internet who will listen.

BillGuard, a New York company founded last year, pools these complaints to help flag fraudulent transactions that affect multiple consumers at once. The company likens its approach to how spam filters work, but there are precedents in financial services as well.

For example, in 2009, the personal financial management site Mint.com (now part of Intuit Inc.) scanned its users' transaction data for a fraud charge that was being widely reported in the news at the time. It found that 800 of its 800,000 users were victims, and sent an alert to those users.

Unlike other PFM providers, BillGuard's system is built around that scenario. "With every new user and every click, the system gets smarter and better at protecting everyone," Yaron Samid, BillGuard's founder and chief executive, said in a presentation Tuesday at FinovateFall in New York.

Though users are encouraged to participate by sharing their fraud observations with the community, "this is not a social network," Samid said. "This is a security company. The interaction with BillGuard is passive."

In addition to direct feedback from its users, BillGuard searches the Internet for complaints about fraudulent charges to help spot the scams its registered users haven't yet caught.

BillGuard also offers a browser add-on that works within banks' online transaction view. The add-on flags potentially fraudulent transactions without requiring the user to leave a bank or card issuer's website. The add-on does not require the bank or card issuer to have a relationship with BillGuard.

The vendor's technology "uses the same techniques that spam filters or fraud filters … use to take advantage of the wisdom of the masses," Bart Narter, the senior vice president of the banking group for Celent, said in an email.

"From a business standpoint, consumers would clearly benefit. Banks might not be as happy about this," he said. "On one hand it is better protecting [banks'] customers; on the other it is going to drive up the number of contested charges, which are expensive for the banks to manage."

Users may also be driven away if too many of their peers falsely flag legitimate charges, Aaron McPherson, a practice director at IDC Financial Insights in Framingham, Mass., said in an email. "I liked BillGuard, although I wonder how many false positives it will generate," he said in an email. "If the user feels bombarded, they will turn it off."