Skip to main content

Attachment Extensions Carrying Malware Banned On Microsoft Outlook

By October 4, 2019May 16th, 2022Cybersecurity

One of the most common means by which malware winds up on the computers of its victims is via an email attachment.  All it takes is one careless moment.  One click to open a file that turns out to be poisoned and you’re in for a world of trouble.

That’s the exact reason why email providers tend to be incredibly selective about what kinds of attachments their services allow.

Microsoft recently announced that they’re further restricting their number of allowable extension types, placing a total of 36 additional file extensions.  That’s thirty-eight new file types you won’t be able to download via Outlook Web, and it brings the total number of blocked file types up to 140.

The company had this to say about the matter:

“We’re always evaluating ways to improve security for our customers and so we took the time to audit the existing blocked file list and update it to better reflect the file types we see as risks today.”

The good news is that you’re unlikely to notice the impact of the new additions, even though it sounds like a big increase.  That’s because most of the extensions the company plans to adopt are fairly exotic and seldom used.  When they are used, at least a significant percentage of the time, they’re used by hackers for nefarious purposes.

Here’s a list of the extensions Microsoft plans to add to the list:

  • .py
  • .pyc
  • .pyo
  • .pyw
  • .pyz
  • .pyzw
  • .ps1
  • .ps1xml
  • .ps2
  • .ps2xml
  • .psc1
  • .psc2
  • .psd1
  • .psdm1
  • .cer
  • .crt
  • .der
  • .jar
  • .jnlp
  • .appcontent-ms
  • .settingcontent-ms
  • .cnt
  • .hpj
  • .website
  • .webpnp
  • .mcf
  • .printerexport
  • .pl
  • .theme
  • .vbp
  • .xbap
  • .xll
  • .xnk
  • .msc
  • .diagcab
  • .grp

Again, most people have probably never even heard of, and don’t use these extensions anyway, so it shouldn’t have a huge or visible impact, but be aware that the change is coming.

Jason Manteiga

Jason J. Manteiga, Vice President of Olmec Systems, has been part of the company for over the past 20 years. He believes that having a great work environment and supportive team, is the ultimate key to success. Since being in the IT realm for over 25 years, Jason, along with Olmec Systems, has been on the Inc. 5000 “List of America’s Fastest Growing Private Companies” and Channel Futures MSP 501 “Top Managed Service Providers in North America,” along with other awards and nominations. Jason earned his Bachelor Degree in Information Systems from the New Jersey Institute of Technology. He also holds certifications in Microsoft MCSE, VMWare VCP, and Cisco CCNA. In his spare time, Jason is a contributor for The Center for Social & Legal Research (Privacy Exchange) and a member of the Morris County Chamber of Commerce. His hobbies include cycling and kayaking. He currently lives in New Jersey with his wife, two daughters and son.