WASHINGTON - A new survey suggests most consumers can't tell legitimate telemarketing calls from cons.

The Consumer Federation of America says nearly 9 in 10 of adults surveyed say they're concerned that telemarketing calls they get from companies they haven't done business with before might be scams.

Susan Grant, who heads the CFA's consumer protection unit, says a little more than half -- 52-percent -- of respondents are on the national do not call registry, while only a third understood what that means: telemarketers are allowed to call only if a consumer on the list has recently done business with them.

Grants says understanding the do not call rules are important, because "legitimate companies usually follow the rules, scammers don't."

The CFA has posted materials on its website to help consumers avoid becoming victims of fraud.