Anti-virus companies have attacked the European Parliament's report on the Echelon spy network which recommends greater use of encryption, warning that encrypted data can hamper virus defence measures.

Sophos has issued a warning to users reminding them that although encryption helps to ensure the privacy of an email, it also has ramifications for virus scanning at the internet and gateway level.

The company pointed out that the only surefire way of scanning encrypted files was at the desktop, effectively compromising the initial layers of security, such as anti-virus on the mail server.

Graham Cluley, senior technology consultant for Sophos, acknowledged that "it's encouraging to see Euro MPs taking privacy seriously. However, companies should think very carefully about deploying encryption because of the impact it may have on their virus protection."

He said that although anti-virus protection at the desktop is about as safe as you can get, those firms which only use "gateway and internet scanning will find detecting viruses inside encrypted email as easy as nailing jelly to the ceiling"

The European Parliament's report set out to dispel the myth that although Echelon exists, it is not capable of intercepting data around the world for the purpose of industrial espionage. However, it also urging companies to begin encrypting their own communications.

"An unencrypted email message is like a letter without an envelope," the report said.