It happened here too. First my Brother HL-5370 printed it, then about 10 minutes later, my HP OfficeJet 7310 printed a slightly different string. They both have the "IEEEMlsqlexec" in common.
Both of our printers have public IP addresses, with the Brother is a bit higher (x.x.x.05) than the HP (x.x.x.02). Looks like some is methodically testing addresses, looking for exploitable machines. Our web servers are higher up and none appear to have been hacked, so I'm guessing (hoping) OS X is impervious to this particular attack.
For what it's worth, this happened to my HP printer (connected via wireless) at exactly the same time, and I have no Mac or other Apple equipment.