Spammers use Word files to bypass filters

As spam filters get better at weeding out unwanted messages, spammers have started inserting their messages inside Microsoft Word documents and attaching them to e-mails.

On Thursday, content security specialists Marshal warned users to beware of Word documents attached to e-mail messages. Unlike executable files, Word documents are commonly exchanged via e-mail and are usually ignored by spam filters.

Bradley Anstis, director of product management for Marshal, told ZDNet Australia that spammers have traditionally avoided sending unwanted messages in a Word -- or similar document -- file because the message sizes are relatively large.

"Most word processors today [can open Word Documents] and historically it hasn't been like that. That is one reason. Secondly, a Word document adds a size and complication to the e-mail going out, which is probably the bigger reason why they have stayed away from this area in the past," said Anstis.

According to a Marshal advisory, the e-mails use a combination of obfuscation and social engineering to create a message that "looks like a typical business e-mail".

"Users open the document expecting to find an invoice or purchase order and instead find a spam message," the advisory said.

Since August 17, Marshal has identified more than 100 examples of this new strain of e-mail spam.