UNDATED - The telemarketing calls are relentless, and come at the worst time - including the middle of the night, according to two people who contacted KATU News about calls they could not stop.

Two local residents, James Johnson of Tigard and Sheryl Juber of Portland, said they were getting calls on their cell phones from telemarketers even though they are listed on the "Do Not Call" list.

Typically, telemarketers abide by the list, but some work very hard to circumvent it. A fine for a violation runs into the tens of thousands of dollars.

The pitch Juber and Johnson received was for extended warranty coverage of some sort, and the calls came in at all hours, including at 3 a.m. The calls came from the same number, listed as a business with a fairly generic name.

Johnson said he thought the callers were pretty dumb to call and leave behind their phone number on his caller ID, so he called back. The number was bogus.

It's a practice known as "Caller ID spoofing" and a man who runs a telemarketing business in Oregon told KATU News that it is one of the tools telemarketers use to mask their identity.

The practice is illegal, but Web sites exist that sell software that let anyone mask their caller ID identity.

The telemarketing owner declined to be identified or go on camera but said he doesn’t have a home phone anymore - because he was sick of getting telemarketing calls.

He showed KATU how telemarketers can shield their identity with easily available computer software that takes little skill to use.

Officials investigating Caller ID spoofing say the best strategy is to string the telemarketer along and if possible and get the name and phone number of the company they work for.

Juber said she tried to get the name of the business calling her but the telemarketer hung up on her after using an expletive.

Officials say people receiving bogus calls should document the calls in any way possible. A complaint can only be filed and an investigation begun if a legitimate business name and number is listed in the complaint paperwork.

Most likely, the telemarketers are well aware of the stipulations.