Freedom Mobile confirmed Tuesday it had a data security breach from late March to late April, but the wireless carrier said only about 15,000 customers were affected — far fewer than an outside research firm's estimate.

The Calgary-based company — which operates networks in Ontario, Alberta and British Columbia — was apparently warned of the breach by researchers at vpnMentor, which announced it to the media.

The vpnMentor report said two of its researchers, Noam Rotem and Ran Locar, had warned Freedom of their findings on April 17, 18 and 23, but didn't get a response from the company until April 24.

"For ethical reasons, we didn't download the database, so we don't know exactly how many people were affected," the blog said.

However, the blog was posted under the title "Report: Freedom Mobile Customer Data Breach Exposes 1.5 Million Customers" based on the assumption that hackers could access unencrypted data from all of Freedom's customer base.

Freedom said in a statement that "any reference to 1.5 million customers affected is inaccurate."

The company said its investigation determined the breach began on March 25 and affected data processed by a new external third-party vendor, Apptium Technologies, that had been hired to streamline its retail customer support.

"The internal systems of Freedom Mobile or [parent] Shaw Communications were not compromised as part of this third-party vendor security exposure," the company said in a statement.

It said the breach affected customers at 17 retail stores who opened or changed accounts as late as April 15 or made changes to opened accounts on April 16. It said the problem was fixed by April 23.

Freedom also said that it had found no evidence, as of Tuesday, that any data has been misused "and we are conducting a full forensic investigation to determine the full scope of impact."

Valerie Lawton, a spokesperson for the federal privacy commissioner's office, said it had received a breach report related to Freedom Mobile late Monday afternoon.

"Canada's federal private sector privacy law, the Personal Information Protection and Electronic Documents Act (PIPEDA), includes confidentiality provisions and we don't have further details to offer at this time," Lawton said in an email.

Under PIPEDA, which was most recently updated in November, private-sector organizations that control personal information must advise the privacy watchdog of breaches that pose a "real risk of significant harm" to individuals.

They must also notify affected individuals about the breaches and keep records.

However, the Canadian law — in contrast to the European Union's year-old General Data Protection Regulation — provides more flexibility about when organizations inform the Office of the Privacy Commissioner.

Asked why it didn't disclose the leak sooner, the company said it took time to verify the legitimacy of the warning and verify details with its third-party vendor.