The theft occurred five weeks ago but only now are those patients being notified. They're from the Chicago area and central Illinois.
Park Ridge police investigated the original theft a month ago, but at the time, Advocate spokeswoman said they weren't sure what was on those computers. Now, they know and they are alerting the media, as well as patients by mail.
There was not much activity at the office building on Touhy Friday night.
But what happened at the Advocate Health Care facility last month is having ripple effect on patients.
"I was floored, because having family members that have been there, I didn't know how far back it went," said Cindy Rickert.
In the early morning hours of July 15th, thieves stole four computers from the administrative office.
The problem Advocate had the personal information of four million patients on those computers.
The information missing includes social security numbers.
"We really wanted to better understand what data and make sure we identified every single patient that could potentially be impacted," said Kelly Jo Golson, Advocate Health Care.
The nearly five week delay in informing patients doesn't sit well with some.
"This is the first time I heard of it. My daughter goes there, I go there. This is a serious violation. Why are we just now finding out?" said LaSahay Sydnor.
"This is an identity thief's greatest dream and a hospital administrator's biggest nightmare," said William Kresse.
Kresse is an associate professor at Saint Xavier's Center for the Study of Fraud and Corruption.
He urges Advocate patients to be vigilant.
"Check frequently your bank statements," he said. "Online is the best way of doing that. Check your credit card statements. Again, online is the best way of doing that. And just question any suspicious entries that you see that you can't understand or identify."
In this case, the information on the computers goes back to the 1990s, so the concern is not only for current patients, but patients that may have died during that time, as well as patients who are disabled or elderly.
Advocate is offering a one-year credit monitoring service for those who may be affected.
For more information: http://www.patientnotice.org/