Outlook Express under threat from hackers

Antivirus firm Beyond Security Ltd. has announced a serious vulnerability within Outlook Express that can bypass the SMTP (simple mail transfer protocol) filtering engines used by many companies, including gateway virus scanners, content filters and firewalls.

Outlook Express allows users to split up sent e-mails, which in turn enables a connecting user to send smaller segments of larger messages in a multiple email.

But the Message Fragment and Reassembly command within Outlook allows anyone, according to Beyond Security, to bypass most of the security restrictions placed on email messages.

As the messages have been fragmented into smaller segments, virus scanners cannot detect them and the recipient will simply receive one large file containing many smaller potentially dangerous emails.

"This generic flaw affects all SMTP content filtering software," said Aviram Jenik, Beyond Security CEO. "As virus writers seek increasingly sophisticated methods to disseminate their viruses, email exploits will become a more popular means for doing so."

Security firm GFI has developed an email security testing engine to allow users to test their systems for the vulnerability.

While several antivirus software vendors have warned users that they could be affected.

"We have confirmed that our product InterScan VirusWall 3.5x is affected by the vulnerability," said a TrendMicro spokesperson. "In order to resolve this problem we have released a patch, which can be downloaded from the FTP server." Users should look for the ISNT Hotfix_build1494_v352_Smtp_case6593.zip hotfix.

Software vendor Symantec admitted it had been aware of the potential malicious use of this feature for some time.

"All currently supported Symantec gateway products, by default, block multipart MIME messages at the gateway. It can be disabled if a multipart email is required," said a spokesman at Symantec. A formal response is due from Symantec today and will be posted here.

"The rejection of segmented emails should be part of a company's comprehensive security policy to restrict potential harmful content from the internal network," he added.

Join the newsletter!


Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Wendy Brewer

PC World
Show Comments

Cool Tech

Toys for Boys

Family Friendly

Stocking Stuffer

SmartLens - Clip on Phone Camera Lens Set of 3

Learn more >

Christmas Gift Guide

Click for more ›

Brand Post

Most Popular Reviews

Latest Articles


PCW Evaluation Team

Aysha Strobbe

Microsoft Office 365/HP Spectre x360

Microsoft Office continues to make a student’s life that little bit easier by offering reliable, easy to use, time-saving functionality, while continuing to develop new features that further enhance what is already a formidable collection of applications

Michael Hargreaves

Microsoft Office 365/Dell XPS 15 2-in-1

I’d recommend a Dell XPS 15 2-in-1 and the new Windows 10 to anyone who needs to get serious work done (before you kick back on your couch with your favourite Netflix show.)

Maryellen Rose George

Brother PT-P750W

It’s useful for office tasks as well as pragmatic labelling of equipment and storage – just don’t get too excited and label everything in sight!

Cathy Giles

Brother MFC-L8900CDW

The Brother MFC-L8900CDW is an absolute stand out. I struggle to fault it.

Luke Hill


I need power and lots of it. As a Front End Web developer anything less just won’t cut it which is why the MSI GT75 is an outstanding laptop for me. It’s a sleek and futuristic looking, high quality, beast that has a touch of sci-fi flare about it.

Emily Tyson

MSI GE63 Raider

If you’re looking to invest in your next work horse laptop for work or home use, you can’t go wrong with the MSI GE63.

Featured Content

Product Launch Showcase

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?