In emailed comments, Sprint spokeswoman Stephanie Vinge Walsh said the company has multiple safeguards to protect customer accounts from intrusion and tampering by unauthorized users.

"It's important to note that there are many different overlapping safeguards in place to ensure our customers' privacy and security, and we have taken steps to further prevent intrusions and spoofing," Walsh said. "While we maintain confidentiality about our security measures, our customer accounts are monitored constantly for several types of activity that would indicate if something illegal or inappropriate may be taking place."

Walsh was responding to questions that arose from a Monday by developer Kevin Burke. In it, Burke detailed how the username and password system used by Virgin Mobile to let users access their accounts online was inherently weak and open to abuse.

Virgin forces subscribers to use their phone numbers as their username and a six-digit number as their password, Burke noted.

Because the password is just six digits long, it is relatively easy to guess using brute-force password guessing tools, Burke claimed. Burke authored a password-guessing tool to crack his own password to demonstrate how easy it is to defeat Virgin Mobile's authentication. The tool was designed to test different 6-digit password combinations until it discovered the right one.