By Rivan Stinson

Kiplinger’s Personal Finance

I recently interviewed Thomas Martin, the president of Martin Investigative Services Inc., based in Newport Beach and author of the recently released book “Seeing Life Through Private Eyes: Secrets From America’s Top Investigator to Living Safer, Smarter, and Saner.”

Q: Why are cellphone numbers popular with criminals?

A: In the mid ’80s, when the cellphone came out, it was used to make phone calls, just like the regular phone in your house. Now our whole lives are on our smartphones. Once criminals get your number, they can get your email, texts, photos, purchases you made online and the credit card information that you used to make those online purchases.

Q: How can crooks get cellphone numbers, and what happens when they do?

A: They can hack the cellphone providers, such as Verizon or T-Mobile, and get batches of cellphone numbers, which can have from 500 to 5,000 numbers in a single loop. Then they send out a text, such as “Here’s $20 off tickets to the local theater,” or “Here’s a $10 gift certificate to In-N-Out,” that contains so-called Trojan-horse malware. Once you click on the link, they have verified your number and have access to your cell data, such as your photos and other information that they can use to try to blackmail you. Or they can capture your date of birth and Social Security number to sell to identity thieves.

Q: You’ve said that crooks can get cellphone numbers from databases, too. Who compiles those databases?

A: The databases that are out there are compiled by all kinds of people. Some online companies sell customers’ data, including cell numbers, and other information about what products people are buying that can be used for marketing purposes. The problem is that cellphone numbers aren’t regulated in the U.S., so there are no rules requiring companies to keep the numbers private.

Q: What can people do to protect themselves?

A: One way is to have more than one mobile phone. Use one phone only for calls — that’s the number you give out. Don’t put any photos on it, don’t text with it, and don’t email on it; save that for the other phone. If having two phones isn’t practical, just be a little more cautious about who you give your cell number to. If you have a landline or work number, it’s better to give those out. If it were up to me, the order would be landline number first, then office number and then cellphone number at the very end.