Bots
Official telegram.org Source
Bots can work in two modes when you add them to groups. By default, bots only see messages that are meant for them. In this case, you'll see 'has no access to messages' in the group members list next to the bot.
Some bots need more information to work, so developers may disable the privacy mode. In this case, the bot will see all messages sent to the group, and you will see 'has access to messages' in the members list next to the bot.
Learn more about privacy mode for bots »
If your group contains very sensitive information, maybe it's better to avoid adding bots you don't trust 100%.
Official Telegram Reference: https://telegram.org/faq
Part of the TGWAY.com Official Telegram Knowledge Base (98 Verified Q&As).