NEW YORK – Text messaging is posing both new opportunities and dangers for America's political campaigns.

The most widely used form of mobile communication, it has become one of the most effective ways for campaigns to reach supporters, using 160-character messages to encourage last-minute donations or provide information such as where to vote. And strict federal rules prohibit such texts from going to anyone who does not "opt in" to receive them.

But some groups have found their way around that requirement, using email – rather than the SMS "short code" that telemarketers normally use – to send unsolicited, anonymous and often negative messages to cellphone lists they purchase through brokers.