A spate of spikes in Japan’s penny stocks is raising speculation the moves were triggered by unauthorized trades.

While smaller firms tend to be more volatile, the frequency and the scale of moves in some of their stocks were causing alarm over unauthorized trades on Thursday. Rakuten Securities Inc., the online brokerage arm of Japan’s e-commerce giant, warned on Tuesday of rising transactions by “malicious third parties” who have obtained login information through spyware and other methods.

Shares of Birdman Inc., a $20 million advertisement company, jumped 33% and then erased the gains all within about 30 minutes on Thursday, with a similar pattern seen in more than 20 other stocks since Wednesday. Birdman did not immediately respond to request for comments on the share move.

A Rakuten spokesperson was not immediately available to comment on whether the share spikes in these companies may have been caused by such transactions.

If the wild swings in these stocks are related to unauthorized trading, “that could undermine market credibility in terms of stock price formation,” said Naoki Fujiwara, senior fund manager at Shinkin Asset Management Trust. While affected individual investors may hold back on investing, the impact as a whole is likely to be limited, he said.

Japan’s Finance Minister Katsunobu Kato declined to comment when asked about the recent moves in penny stocks at a regular briefing in Tokyo.

Japanese retail investors have been opening up so-called NISA accounts, a tax-free investment program, with households investing more of their cash as rising inflation hurts their savings.

Written by: Yasutaka Tamura — With assistance from Takashi Umekawa @Bloomberg

The post “Japan Penny Stocks Spike, Fuels Worry of Unauthorized Trades” first appeared on Bloomberg