  In this article, we study a variant of the minimum dominating set problem
known as the minimum liar's dominating set (MLDS) problem. We prove that the
MLDS problem is NP-hard in unit disk graphs. Next, we show that the recent
sub-quadratic time $\frac{11}{2}$-factor approximation algorithm \cite{bhore}
for the MLDS problem is erroneous and propose a simple $O(n + m)$ time
7.31-factor approximation algorithm, where $n$ and $m$ are the number of
vertices and edges in the input unit disk graph, respectively. Finally, we
prove that the MLDS problem admits a polynomial-time approximation scheme.
