Many users of Tencent's QQ instant messenger took to social media to complain that hackers have accessed their accounts and sent porn-related advertisements to their contacts since late June 26.

Some users mentioned on the Weibo microblog that they were instantly removed from many group chats as the administrators thought they were spammers, bringing them inconvenience and "a level of shame."

One Weibo user said the administrator of one group decided to put on a "curfew" and temporarily banned all members from posting in the group, only to find the admin account posted a porn ad later.

Spreading pornographic content is illegal in China, and a severe offense could lead to prison.

QQ staff on Monday posted an announcement on Weibo saying they received much user feedback about "QQ account being stolen" at around 10:00 p.m. on Sunday and then launched a security inspection.

The staff said the root cause is "users scanning fake QR code for video game login," which allowed hackers to hijack their accounts to spread ads.

"Affected accounts have gradually returned to normal" since early Monday, said the announcement.

The staff apologized for the inconvenience users experienced and warned that users should not scan QR codes from unknown sources.

Many Weibo users joked about the incident when replying to the QQ staff post.

"I was a decent man until 1:00 a.m. today," a user said.

Others said they were not satisfied with the official reply, adding that the QQ team could have done better to protect user accounts.

China's internet giant Tencent has struggled to control such illegal access to QQ accounts since the beginning of the service, dating back to 1999 and has been loved by youngsters since.

Before the company's WeChat ruled China's mobile internet, QQ was the app that dominated young people's lives on the PC internet.

In the early years of QQ, account safety was hard to keep. Many Chinese teenagers once considered the ability to steal other people's QQ accounts as a quality of a good hacker, which later turned into a meme about stereotyping computer engineers.

(Cover via CFP)