Got a call from this number today, the caller claimed to be from Medco. I began using Medco 2 days ago after a several year hiatus; the rep knew what day I placed the order and knew the correct invoice #.
The caller definitely had access to Medco's internal database, and only asked for my current address
Seems legit to me.

Received a call from this number, they left a message informing me that Medco needed to verify my address. I recently moved and have also just signed up to get my prescriptions via Medco. The message gave me another number to call back, Medco's main number. I called the number and had to verify my new address for my current prescription. They did not ask for credit cards or SS numbers.

said they were medco calling about an order and gave 866-686-3326 to call back M-F 9 am - 5 pm (didn't say time zone) and left a # to reference which seemed kind of long. also said could leave a msg is calling at a different time. Definitely was not the normal type of calls I get from Medco, nor either of the phone numbers I have saved for them which I know are good: 866-383-7314 and 800-903-3589.
I sent a message on thru Medco's website to see what the deal is.

I received a call from this number and it was a woman who left a message. It is Medco, but the person they were looking for was not me. So they are not careful how they dial or do not listen to my message as it clearly states my name. Yeah, a company I might want to do business with

I received a call from this number today and it showed up as "unknown"  interestingly, just yesterday I conducted business with MEDCO for refilling some Rxs.  I did it online and updated my profile with credit card # and other details.  I went back to my cell phone call log and found that this number had called me also the day after my previous Rx refill, which required me to go online and request a refill.  I suspect someone at MEDCO has been stealing policy holder's data for what ever scheme they are conducting.  Anyone with a legitimate business is not going to hide their caller ID identity.  I am thinking of contacting MEDCO and providing them with a print out of this site because as I read below this goes back to 2009.  Its a shame that MEDCO doesn't have in place safeguards to prevent sensitive customer data to stolen from their data bank which includes no other than social security numbers, date of birth and everything an identity thief would need to take on someone's identity.