According to CNet News.com, a staff memo announced the prohibition, saying:
"We believe it is appropriate for that policy to be extended throughout the firm, without exception, to help ensure that electronic communications to and from Merrill Lynch facilities are subject to proper monitoring and surveillance."
The ban extends to non-company message boards, chat rooms, forums and e-mail accounts.
E-mail is perceived as a serious weakness in the fight against computer viruses and Merrill Lynch is only the latest organisation to crackdown on its employees' use of third party e-mail services. Goldman Sachs has a similar policy, and both companies have signed up for specialist, secure instant messaging systems.
The regulatory environment, particularly for investment and financial institutions, demands that electronic communications be treated with the same weight as any other form, and companies are increasingly concerned to make sure that e-mail and instant messages are monitored and archived or banned.