SAN FRANCISCO (CBS) – Business seems to booming for text message spammers. However, there are ways you can prevent them from reaching your cell phone.

Kent German with CNET said, in the last few years, spam by phone has skyrocketed.

“Spammers are learning,” German said. “It’s a new avenue for people to communicate, sell things, and get out advertisements.”

German added that spammers are able to obtain phone numbers through several different sources.

“Any time you enter you phone number and you buy something, enter a political donation, those sources could sell your phone number,” he said.

Still, experts suggest never replying to unfamiliar numbers and adding your phone number to the do not call registry.

AT&T, Verizon and Sprint offer free online options that allow consumers to block specific numbers.

T-Mobile charges $4.99 to block phone numbers.

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