ATM Systems, which is based in Maryland, said someone who has insider knowledge is likely involved in the thefts. A master code has apparently been passed on to people in Chicago, who can now access the machines' software.
The spree, which ran from December to January, did not impact individual accounts. The master code let the thieves program the ATM to hand out $20 bills instead of $1 bills. For instance, a $100 withdrawal on a generic gift card would mean 100 $20 bills instead of 100 $1 bills.
Crimestoppers said three men are responsible for taking $140,000 from several independent ATMs operated by ATM Systems in the downtown River North neighborhood. Crimestoppers is offering a $1,000 reward for information leading to the arrest of any of these men.
"We know that in a couple of the pictures people should be able to recognize who they are. Take a look at your neighbors. Take a look at your co-workers. If you think you know who did this crime, call the 800 number," said George McDade, Crimestoppers.
Police said no personal accounts were compromised. ATM Systems said affected machines were re-set so it would operate normally with subsequent customers.
Security consultant Joel Dubin works on ATM code issues with banks and says what happened with the independent machines is typical of how cyber crime is segmented.
"You have these organized criminal rings that are the professionals the brains behind the whole thing, writing the code, doing all the hard work and they can give it to the street level grunt and all they need to do is go, here's the code, go to the machine and do what you need to do," said Joel Dubin.
ATM Systems acknowledges it has a problem with someone leaking critical codes. A company spokesperson said they buy their machines from the same manufactures banks use.