"I have to tell you that sadly this affectionate greeting contains a virus which has immobilised the House's internal communication system," he told MPs.
Companies as varied as Express Newspapers and the giant Scottish Power have been hit, along with small companies, universities, city institutions and even parts of the NHS.
Sarah Perkins of PC Pro magazine estimated that by midday on Thursday up to 10% of UK businesses had been affected in some way.
The news that MPs at Westminster had been cut off from e-mail contact with the outside world was confirmed to the House of Commons by shadow Commons leader Sir George Young
"I have to tell you that sadly this affectionate greeting contains a virus which has immobilised the House's internal communication system," he told MPs.
"This means that no member can receive e-mails from outside, nor indeed can we communicate with each other by e-mail.
"Up to this moment, no cure has been identified."
Some of the biggest firms in the country have been hit.
Thousands of users at Scottish Power were ordered to log out of e-mail and internet services after the virus arrived in the Glasgow headquarters on Thursday morning.
"Our IT staff are working to clear out the system," said a spokeswoman.
Costing 'millions'
"They are continuing to work their way through, but we are still down at the moment. They hope to have things restored later today."
At Express Newspapers, staff were warned in a tannoy announcement mid-morning not to open Iloveyou e-mails.
Staff were left with the rogue bugs sitting on the screens, waiting for further instructions.
Some of the e-mails also arrived at BBC offices in London, and staff were warned not to open them.
Sky News, publishing firms, public relations companies, and City of London institutions have all been hit.
One computer expert, Graham Cluley of Sophos, says the cost to businesses will almost certain run into millions of pounds.