Curoisity I'm wonering about: What triggers "fraud alert" errors on card transaction?

[uncredited]

I think I've only had one or two "fraud alert: did you really make this purchase" type things in my life over all the years.  Just happened to use my Citi card with a vendor I've used it for multiple times before in the past 5 months, and it declined the transaction and sent a text, email, and app fraud alert, do you recognize this transaction message.  All was good after hitting yes and reprocessing the checkout, but it made me wonder what actually triggers these things when the same card used at the same merchant multiple times over months can spontaneously trip a fraud trigger?

[CCrew]

Information Security professional here, and have multiple financial services clients. A fraud hit can either be 100% random, or AI driven based on frequency/size of average transactions. There are algorhythms behind it all of which are specific to the institution. You're not being singled out :-)

[uncredited]

---

@CCrew wrote:

Information Security professional here, and have multiple financial services clients. A fraud hit can either be 100% random, or AI driven based on frequency/size of average transactions. There are algorhythms behind it all of which are specific to the institution. You're not being singled out :-)

---

That's kind of what I figured.  Random may well be it.  This was a surprising one.  The amount, for me was within normal (in fact smaller than a transaction with the same merchant a month ago that raised no alert), not sure where average is, but it's not an "atypical looking" transaction or anything in terms of amount or vendor.  I've had much larger transactions on the card, sometimes with new merchants instead of repeat ones, but this transaction is the first to hit a fraud flag, so I was surprised by this one.  I assumed the decline was that I messed up entering the expiry or something, which happens, and then heard my phone ding with the alert and was like "huh....didn't expect that...." Thankfully it was just a text reply and all was well and not some actual hassle. But definitely surprised me and made me wonder what goes into that.

[wasCB14]

In my experience the algorithms have been pretty inaccurate with Discover and Chase.

e.g. I live in California. Discover declined a $150 clothing purchase 20 miles away, but Chase allowed a charge from "Liberty Television Puerto Rico" or something like that.

[NoMoreE46]

I have had only two myself.  One was with my Amex at Home Depot.  The other was a Citi card denial at Burger King.

My kid wanted a second set of nuggets.  My Custom Cash card was denied for $2.10. 

Later on, I looked at my Citi app/text messages and saw that the denial was based on a possible "duplicate charge" scenario.  

[uncredited]

I may have figured out some of what triggered it. Something about the merchants processing system must have changed, I checked an old statement from September and it shows the transaction as company name and phone (company name 8005556666).  On the current pending charge from today it shows as "company name city ST" instead.  Still doesn't really explain why it would have generated a fraud flag at all, but it does explain that it doesn't see it as a merchant I've used before and that something about whatever payment processor they must have changed to may somehow have made it look suspicious.

[CashOutReFi]

My guess would be the merchant name or sales category was changed, failing to connect the latest (failed) charge with the prior transactions. 

-

Things I've personally experienced:

Used a card to panic fill all 3 vehicles before a gas crisis left us with none at our local station. The third transaction was flagged as fraud and declined until I called to reactivate the card. 

-

Things other people have experienced:

https://m.youtube.com/watch?v=HkZNddd9Pxc