Security experts are warning about a stealthy Windows virus that steals login details for online bank accounts. Experts say the virus is dangerous because it buries itself deep inside Windows to avoid detection. The malware, called Trojan.Mebroot by Symantec, installs itself on the first part of the computer's hard drive to be read on startup, then makes changes to the Windows kernel, making it hard for security software to detect it. Criminals have been installing Trojan.Mebroot, known as an MBR (master boot record) rootkit, since mid-December, and were able to infect nearly 5,000 users in two separate attacks, staged on Dec. 12 and Dec. 19, according to Verisign's iDefense Intelligence Team. In order to install the software on a victim's computer, attackers first lure them to a compromised Web site, which then launches a variety of attacks against the victim's computer in hopes of finding a way to run the rootkit code on the PC.