There's also supposed to be a phone scam going around. Some randomer calls and during the call asks "Can you hear me?" When you say "Yes", your "Yes" is recorded and can, apparently, be used to give your "consent" to spending lots of money on nothing.

However, Snopes http://www.snopes.com/can-you-hear-me-scam says it's "unproven"… use your judgment.