If you work in an office and recently have seen your printer suddenly start creating documents out of the blue, you are not alone. According to an update on the Symantec web site this week, a recent outbreak of a PC malware program called Trojan.Milicenso might be to blame.
The malware is supposed to target PCs. Symantec says that for the past two weeks, the trojan has made itself known mostly in the US and India, along with parts of Europe and South America. It's delivered through the normal channels for malware; either from a person surfing to an infected web site or opening an email attachment.
However, it seems that this malware can also affect printers that are hooked up to the infected PC. Symantec says that it has received "multiple reports of massive print jobs being sent to print servers, printing garbage characters until the printer runs out of paper."
The malware generates an .spl file when it infects a PC. Symantec says:
The .spl file, while appearing to be a common printer spool file, is actually an executable file and is detected as Adware.Eorezo. Depending on the configuration, any files, including binary files, created in that folder will trigger print jobs. This explains the reports of unwanted printouts observed in some compromised environments. Based on what we have discovered so far, the garbled printouts appear to be a side effect of the infection vector rather an intentional goal of the author.
So if you happen to see your office printer generate a ton of nonsensical content, you might want to call the IT teammate rather than just a printer technician.
Source: Symantec website