Wallet and block exploring service Blockchain.info has upgraded its security, apparently in response to a phishing campaign.

The company has beefed up the security on its Android wallet app, adding a PIN to the application to stop people from unauthorized access.

According to reports from users, the company has also begun notifying people who attempt logins from untrusted computers. It asks them to confirm their login attempts, and informs them of the time, the IP address and the browser type being used to request access.

"If this login attempt was not made by you this email can be safely ignored however be aware someone may know your wallet alias," the email reportedly says.

The change has highlighted some security problems for users. "What about if I received 14 such emails?" Asked one user on the Blockchain.info Twitter feed. Others in Reddit discussions reported having similar issues.

On April 23, Blockchain.info posted a message on its Twitter feed thanking hosting firm Bitronic Technologies for terminating several phishing sites that had attempted to scam Blockchain.info users to gain access to their accounts.

Blockchain.info also suffered from a DDoS attack earlier in April.