The messages included ASCII art depicting robots and warned that the printers had been compromised and they were part of a botnet . The hacker , who uses the online alias Stackoverflowin , later said that the botnet claim was not true and that his efforts served only to raise awareness about the risks of leaving printers exposed to the internet . Stackoverflowin claims to be a high-school student from the U.K. who is interested in security research . He said that Vulnerability-related.DiscoverVulnerability for the most part he simply sent print jobs using the Line Printer Daemon ( LPD ) , the Internet Printing Protocol ( IPP ) and the RAW protocol on communications port 9100 to printers that did n't require authentication . However , he also claims to have exploited Vulnerability-related.DiscoverVulnerability an undisclosed remote command execution ( RCE ) vulnerability in the web management interface of Xerox printers . The hacker estimates that up to 150,000 printers were affected Vulnerability-related.DiscoverVulnerability by his effort , but claims to Vulnerability-related.DiscoverVulnerability have access to more RCE flaws that he did n't use and which would have allowed him to print to over 300,000 printers . As printers around the world started printing the hacker 's rogue messages on Friday , affected users took to Twitter to report the problem . From the photos they posted , it appears that many of the printers were part of point-of-sale systems . The issue of publicly exposed printers is not new and has been exploited Vulnerability-related.DiscoverVulnerability before to print rogue and sometimes offensive messages . However , the issue was renewed last week when researchers from Ruhr-University Bochum in Germany published a paper Vulnerability-related.DiscoverVulnerability on different attacks against network printers and an assessment of 20 printer models .