A former bookkeeper who embezzled more than $750,000 from her employer and filed false tax returns was sentenced to three years in federal prison, the U.S. Attorney's Office for the District of Alaska said Wednesday.

John Light, owner of Western Construction and Equipment in Anchorage, described in an interview Wednesday how he caught Raenette K. Yangson, who was forging checks in his family's name.

Light said he discovered the false checks only when his computer became infected with a computer virus.

Yangson, 42, embezzled around $753,000 from the company, where she worked as a bookkeeper from 2006 to 2013, court documents show.

During those years, Yangson wrote 405 forged checks, Light said.

Yangson wrote the checks to herself and her husband. Then, Yangson changed information in the company's accounting system to make it appear as though she had issued legitimate payments to other companies, Light said.

An IRS audit during those years didn't catch her, and neither did other annual audits, Light said.

But then Light's grandson downloaded a computer virus on to Light's home computer.

His computer was connected to the business network, and with the virus in place, Light wasn't able sign off. That, in turn, prevented Yangson from going into "single-user" mode in the accounting system and secretly manipulating the books, Light said.

So Yangson tried something else, Light said. She balanced the books by recording a $14,000 discrepancy as "fees." But it was the wrong time of year for the company to be paying those kinds of fees, Light said.

"I saw those. I said, 'There's no way we have those fees,' " Light said.

Light pulled up the check and saw it was written to Yangson's husband. With the help of a few other people, he started reviewing the business's checks — more than 400 checks a month covering over six years.

"We did all the forensic accounting stuff in-house," Light said. Then they turned over the information to law enforcement.

Yangson has been ordered to pay restitution with the final amount to be decided at a later date, but Light is not expecting to get it all back.

Yangson must also pay the IRS roughly $206,000 in taxes owed on the stolen money, according to federal prosecutors.