The gateway security company had its research arm, the IronPort Threat Operations Center, study the effects of these nuisance messages. The result of bounced malicious messages that have forged return addresses, and they are becoming a bigger threat to businesses, said IronPort representatives.
"When a spammer is sending out ten million spam messages per day, 20 percent or more will bounce because of invalid addresses," the report said. "Since the spammers don't want to deal with two million incoming bounce messages, they typically forge the return address and the bounces become 'misdirected' or returned to an innocent third party that had nothing to do with the spam in the first place."
IronPort found that misdirected bounces make up nine percent of all global email. Considering that legitimate mail makes up 20 percent of the pie, it is clear that misdirected bounces are becoming a bigger threat. As the number of these messages increase, the threat they pose to disrupting business also grows.
Bounces are more than annoyance to business, as a large number of them can be enough to cause a massive distributed denial of service (DDoS) attack that can bring down even the most mature email systems. Researchers at IronPort discovered that more than 55 percent of all Fortune 500 companies have experienced a disruption of service or a total denial of service (DoS) due to misdirected bounces. The cost of such system outages is unquantified, but IronPort estimated that it worth billions of dollars.
Misdirected bounces also account for damages in another more quantifiable area. When unsuspecting users receive messages telling them that a message that they never sent in the first place was bounced due to an attached virus, they usually become concerned enough to contact the help desk. This resulting drain on IT resources totals up to more than $5 billion a year, the report found.