July 30 (Reuters) - Chinese mobile security software maker NQ Mobile Inc said it received a buyout offer from investment firm Bison Capital Holding Co for about $490 million.
The non-binding cash offer of $9.80 per American depository share was at a premium of 42 percent over NQ Mobile's Tuesday close. NQ Mobile shares rose as much as 22 percent.
In May, NQ Mobile sold a small stake in its unit, FL Mobile, to China's Bison Capital for about $15 million.
The Chinese software company, which has been accused of fraud by short-seller Muddy Waters Research Group, said its board was reviewing the proposal.
NQ's stock has been volatile since Muddy Waters made the allegations in October, plunging from a high of $25.90 just before the report was released to a low of $3.45 this month.
NQ shares closed up 8 percent at $7.44 on the New York Stock Exchange on Wednesday.
(Reporting by Supantha Mukherjee in Bangalore)