Texas man David Lu, 55, began to sabotage his employer’s systems after being effectively demoted in 2018, according to the US Department of Justice.

The under-appreciated programmer was terminated in September 2019, automatically activating his secret code and costing the business hundreds of thousands of dollars in losses.

Among his secret changes was the introduction of a “kill switch” designed to lock out all employees if his own login credentials were deleted.

This kill switch was labelled “IsDLEnabledinAD”, an abbreviation of “Is Davis Lu enabled in active directory” — effectively signing his work.

Other changes were designed to slow or crash the computer systems and were labelled “hakai”, the Japanese word for “destruction”, and “hunshui”, a Chinese word for “sleep” or “lethargy”.

Lu was convicted by a US federal jury last week of causing intentional damage to protected computers, for which he faces a maximum penalty of 10 years in prison.

A sentencing date has not yet been set.