The president of London Drugs has issued a letter apologizing for a cybersecurity incident that forced the company to close stores for more than a week, but he says there's no evidence customer databases were compromised.

The letter from Clint Mahlman says the Richmond, B.C.-based company is still investigating the April 28 incident, and should it find that any customer information was affected, it would inform people according to privacy laws.

Mahlman says London Drugs works with experts to ensure its systems are secure, and independent auditors regularly review the company's security practices.

But he says no organization can be completely safe from rapidly evolving cybersecurity threats and breaches orchestrated by "sophisticated" attackers.

He says the retailer and pharmacy immediately shut down all 79 of its stores throughout Western Canada as soon as the "suspicious activity" was discovered, and the reopening process followed the company's established protocols.

London Drugs says all stores had reopened by Tuesday.

Mahlman thanked customers for their patience, as well as London Drugs employees for dedication they showed during a challenging time.

"We even had experienced retired employees show up to lend a hand given their considerable experience and historical knowledge," the letter adds.