Companies have failed to learn the lessons from last year's damaging Love Bug virus, analysts said.
The self-replicating virus, which sent itself to every address book entry when opened, was attached to an e-mail titled "check this out" which promised pictures of tennis star Kournikova. It is thought to have originated from an ISP address in the Netherlands.
As well as mass mailing from an infected system which overloaded communication channels, the Kournikova virus activated the default Internet browser and directed it to the Web site of Dynabyte, a Dutch computer reseller. A Dynabyte spokesman said the virus did not seriously affect business, but that the company was investigating reports that the virus had been launched by a disgruntled former employee.
Last year, the Love Bug virus caused an estimated $10bn (£6.7bn) in lost business productivity, according to US-based analysts.
"To give an idea of the scale of this thing, one company received 4,500 of these [Kournikova] e-mails overnight outside office hours," said Graham Cluley, senior technology officer at Sophos Anti-Virus.
Cluley advised that firms set up an e-mail gateway stopping any double extension or VBS file - the Kournikova virus had a JPeg and VBS file attached - "whether they are viruses or not".
"Companies do not do enough to emphasise the importance of security," said Tony Lock, an analyst at Bloor Research.