Shares in Twitter (NYSE: TWTR) fell on Monday after the tech group warned of “unusual activity” from China and Saudi Arabia.

After the group discovered unusual traffic that may be linked to hackers while investigating a security bug where data was exposed.

Twitter said in a blog: “We have become aware of an issue related to one of our support forms, which is used by account holders to contact Twitter about issues with their account. We began working to resolve the issue on November 15 and it was fixed by November 16. This could be used to discover the country code of people’s phone numbers if they had one associated with their Twitter account, as well as whether or not their account had been locked by Twitter.”

“While we cannot confirm intent or attribution for certain, it is possible that some of these IP addresses may have ties to state-sponsored actors. We continue to err on the side of full transparency in this area and have updated law enforcement on our findings,” it added.

Shares in the group fell almost 7% on Monday, the biggest fall in over two months.

In October of this year, Twitter posted a profit for Q3, sending Twitter shares up.

Michael Pachter, who is an analyst at Wedbush, said the risk of hackers has impeached trust for many users.

“Clearly, a breach like this impairs user trust in the platform,” he added.