Contracts negotiated on email or other electronic means of communication are binding, ITT delegates were warned.
David Willbe, counsel at international legal firm Crowell and Moorings, addressed the annual overseas event for senior executives, about the impact of technology on contract law.
He said even media like Twitter and Youtube could be vehicles for agreeing legally binding contracts which do not need to be physically signed to be valid.
Willbe said the web has shifted the balance in favour of convenience in how contracts are created but that this has raised some potential problems for firms.
A court case involving a customer of financial spread betting firm Spreadex recently found in favour of the customer who claimed he could not be held responsible for bets placed by someone else after he left his computer on.
Willbe said the case indicated courts would look unfavourably on any terms and conditions that unfairly binds the customer into the contract which were not obvious to the customer.
"The law says people are not reading online terms and conditions. Where I think this leads us to is a summary. Anything particularly important in there you absolutely need to stand up you will probably have to put it on you website and make it really obvious."