Barracuda customers left high and dry

A faulty antivirus update left thousands of Barracuda Networks' customers without email for hours on Tuesday.

More than three-quarters of the spam firewall company's 35,000 customers were affected by the hitch, Barracuda said. Their systems downloaded an incomplete antivirus update file just before 05:00(PDT) and, as a result, their Barracuda appliances stopped all email traffic and stored messages in a queue. A fixed file was sent out and service was fully operational about two hours later, the company said.

Stephen Pao, vice president of product management for Barracuda, said: "What we have built in to our spam firewalls is a protection mechanism, so that when an incomplete virus definition comes through the system, it will queue the email rather than send it. It hangs out and waits for the next virus update."

Barracuda is known for affordable anti-spam appliances for businesses. The company stressed that the hitch was not an outage, as systems were actually working.

A company spokeswoman said: "The precautionary feature is not just there for incomplete virus definitions caused by operational issues at Barracuda Networks but it also serves as a precautionary feature for sources from which we cull external virus definitions." Virus definitions are the "fingerprints" that defensive systems use to try to identify malicious software.

So many customers were affected because most use the virus-scanning capability and subscribe to Barracuda's hourly virus updates, the company said.

An operational version control issue with the update caused a partial definition to be downloaded on Tuesday, Pao said.

The Barracuda Spam Firewalls themselves were not breached by a virus, nor was Barracuda's system actually out for any period of time, Pao said. Customers were not exposed to any threats in any way while the system kept email in a holding pattern, he added.

Candace Lombardi writes for CNET News.com