Organisers of the annual June 4 vigil had their e-mail accounts swamped yesterday in a hacking attack which appeared to come from the mainland.
The official e-mail account of the Alliance in Support of Patriotic Democratic Movements in China is usually hacked in the lead-up to the anniversary of the Tiananmen Square crackdown.
But members said the attacks came early this year, and protest organiser Richard Tsoi Yiu-cheong said it was the first time individual accounts had been attacked.
He said they were "observing" the situation and would call the police if the attacks do not stop.
The e-mails, most from mainland domains and many containing simplified Chinese characters used on the mainland, started arriving at 10am yesterday.
Tsoi, one of six core members to receive the e-mails, said the alliance's official e-mail account is subject to hacking every year ahead of the anniversary "but … the hacking began much earlier this year, even on the official site".
The core group, including legislator and chairman Lee Cheuk-yan and lawmaker Albert Ho Chun-yan, use different e-mail providers, he said.
Tsoi said the hacking could constitute an offence of repeated harassment.