The Amazon buckets were discovered by security firm UpGuard on 13 May and the findings were detailed in a rather verbose blog post on Friday.
Attunity was notified the same but due to time zone differences it took until the following day for access to be shut off.
The company's website claims that it has about 2000 business customers which span half of the Fortune 100 list.
There were also numerous files containing credentials for various Attunity internal systems and the password for the corporate Twitter account was exposed in plaintext in an email.
"Attunity’s business is to replicate and migrate data into data lakes for centralised analytics," UpGuard said.
"The risks to Attunity posed by exposed credentials, information, and communications, then are risks to the security of the data they process. While many of the files are years old, the bucket was still in use at the time detected and reported by UpGuard, with the most recent files having been modified within days of discovery."
In a statement, a spokesperson from business intelligence and visualisation software provider Qlik, which acquired Attunity recently, said: "Attunity was notified in-mid May of an issue related to internal company data stored in AWS S3 buckets.
"Attunity personnel responded quickly to ensure that the data was secured. Attunity customers deploy and operate the software directly in their own environments, and therefore Attunity doesn’t store or host sensitive customer data.
"Following Qlik’s acquisition of Attunity in May, and upon becoming aware of the issue, Qlik applied its security standards and best practices to the Attunity environments, including monitoring by Qlik’s 24x7 security operations centre.
"We are still in the process of conducting a thorough investigation into the issue and have engaged outside security firms to conduct independent security evaluations.
"We take this matter seriously and are committed to concluding this investigation as soon as possible. At this point in the investigation, indications are that the only external access to data was by the security firm that contacted us."