of questionable origin （指物）; of dubious background （指人）

他挣的钱来路不正。

He obtained the money by dishonesty.

正路不走偏走斜路

turn from the right road and take the wrong one -- give up an honest life for a dishonest one

这笔钱来路不明。

This sum of money is of questionable origin.

来路不明的飞机

unidentified aircraft