A snapshot of e-mail activity from security company MessageLabs found the number of customer e-mails it monitored grew from the average of 500,000 to 1 million an hour after .
"Sometime after 9:00 a.m. BST (1 a.m. PDT) we saw e-mail traffic rise," said Alex Shipp, senior antivirus technologist for MessageLabs. "That's ignoring spam--that's half a million legitimate e-mails an hour up to 1 million.
"We don't know what the traffic is, but we're guessing that it's 'Are you OK?' and 'Have you seen the news?' messages. But that's based on the e-mails we've been getting."
Vodafone, the U.K.'s largest mobile operator, is asking customers to avoid using their phones following the attacks. All the United Kingdom's mobile phone networks wereby the sudden rise in calls and text messages early Thursday morning.
At least 45 people were killed when three bombs exploded on the London Underground train network and a fourth detonated on a double-decker bus, according to Sky News. London hospitals have reported at least 300 wounded so far.
Prime Minister Tony Blair condemned the attacks. Other leaders of the G8 countries, who are currently meeting in Scotland, supported Blair.
London Mayor Ken Livingstone has described the attacks as an "indiscriminate attempt at mass murder."
A group calling itself the "Secret Organization of al-Qaeda in Europe" is reported to have posted a message on a Web site claiming responsibility for the attacks. London police said no groups have contacted them claiming responsibility.
Dan Ilett of Silicon.com reported from London.