Ever hit the "reply all" e-mail button at work accidentally?
Well, you have probably never had it as bad as one of Britain's National Health Service (NHS) staff. The employee unwittingly fired off the message on Monday (Nov 14) morning without realising that the e-mail was sent to 840,000 co-workers, reported the BBC.
The mistake quickly clogged up the system and was ironically worsened by users hitting "reply all" to complain.
The distribution list was disabled at 10am, but some users continue to have problems.
The secure e-mail system is utilised by NHS staff and other approved organisations to discuss healthcare and related activities.
"It's driving me bananas," one doctor, who requested not to be named, told the BBC.
"The thing is hundreds of people have been replying to all.
"My NHS e-mail is very important to me because it's the only secure way I can send and receive anything safely about my patients.
"So, this is a major problem (and) potentially a risk to patients."
A spokesman for NHS Digital said it was not anyone from the IT team who had sent the unfortunate message, but declined to identify the culprit, saying he or she was not to blame.
"A number of e-mail accounts have been operating slowly," said NHS Digital in a statement.
"This was due to an NHS Mail user setting up an e-mail distribution list which, because of a bug in the supplier's system, inadvertently included everyone on the NHS Mail list.
"As soon as we became aware of the issue, we deleted the distribution list, so that no-one else could respond to it.
"We anticipate the issue will be rectified very soon."