For philanderers in Japan, the latest tech isn't necessarily the best when it comes to keeping their partners in the dark, according to a Wall Street Journal report.

Fujitsu's "F-series" phones, first released 11 years ago, dubbed "uwaki keitai" ("infidelity phones"), have become a go-to part of any Lothario's arsenal, since it's able to hide calls, text messages and emails from designated contacts by inputting a code. Any calls from private contacts are also unrecorded in the phone's records while in "privacy mode." The phones are only available in Japan.

"If Tiger Woods had this Japanese feature in his phone, he wouldn't have gotten in trouble," said Takeshi Natsuno, who insisted on beefing up Fujitsu's security features while working at Fujitsu's partner company, NTT DoCoMo, at the time.

Natsuno said the extra privacy was a response to hearing about couples breaking up over incriminating evidence found on cell phones.

A Fujitsu spokesperson acknowledged the company's efforts to boost security, but did not comment on the "infidelity phone" nickname. However, attempts to bring some of those features into its smartphones have been criticized; the newest version of "privacy mode" requires users to get a separate app, rather than use the phone's built-in settings.

"It's totally useless," one local blogger said in rejecting the new version. "I hold out hope that Fujitsu adds the real privacy mode with its next smartphone."

To see how "privacy mode" can help shady lovers cover their tracks, watch this video by the Journal, published Jan. 11, 2013.