According to a report in Engadget, these spams show up under the "Top" tab of Twitter's trending section and are "even more brazen in their attempts to lure in gullible readers".
Once clicked on these accounts, the users are taken to porn sites, asking for personal information, including email address, age, location and credit card number.
Since these spams are seen under the "Top" tab of the trending section, people see them first when visiting any key trending topic.
"All the accounts were created in August and they used the 'Pinned Tweet' feature of the app to try to promote a website," said the report on Wednesday.
For example, a bot with the handle @calvi_anna said: "My WhatsApp is on the site in the profile information about me, call me. Watch my private videos for free after a simple registration".
Once you click, you are redirected to porn sites.
"Some of these are the same sites you'll come across when you fall for a scheme from the bots leaving comments on Instagram, except on Twitter they're using trending topics to run their operation, the report added.
In a statement, Twitter said it is working hard to ensure this type of spam does not appear in search results or conversations.
"Sometimes, it can miss these dubious accounts and when that happens, people do have the option to report them," Twitter told Engadget.
The appearance of such porn bots on Twitter's trending topics comes at a time when the feature is already under scrutiny.
The feature has been "blamed for gaslighting conspiracy theories about Jeffrey Epstein, the American millionaire and convicted sex offender who recently committed suicide in a New York City jail".
According to Twitter's "Sensitive Media Policy", you may not post media that is excessively gory or share violent or adult content within a live video or in profile or header images. Media depicting sexual violence and/or assault is also not permitted.
"Adult content is any consensually produced and distributed media that is pornographic or intended to cause sexual arousal," reads the policy, adding that "If you share this content within Tweets, you need to mark your account as sensitive".
( With inputs from IANS )