Lass.exe is related to Win32.Rbot, an IRC controlled backdoor. Backdoor Trojans
are very dangerous
because they provide a means of accessing a computer system that bypasses security mechanisms and steal sensitive information like passwords, personal and financial data which they send back to the hacker. Remote attackers use backdoor Trojans as part of an exploit to to gain unauthorized access to a computer and take control of it without your knowledge. Read the Danger: Remote Access Trojans
If your computer was used for online banking, has credit card information or other sensitive data on it, you should immediately disconnect from the Internet until your system is cleaned. All passwords should be changed immediately
to include those used for banking, email, eBay, paypal and online forums. You should consider them to be compromised
. They should be changed by using a different computer and not the infected one. If not, an attacker may get the new passwords and transaction information. Banking and credit card institutions should be notified of the possible security breach. Because your computer was compromised please read How Do I Handle Possible Identify Theft, Internet Fraud and CC Fraud?
Although the backdoor Trojan has been identified and may be removed, your PC has likely been compromised and there is no way to be sure the computer can ever be trusted again. It is dangerous and incorrect to assume that because the backdoor Trojan has been removed the computer is now secure
. Many experts in the security community believe that once infected with this type of malware, the best course of action is to wipe the drive clean, reformat and reinstall the OS. Please read "When should I re-format? How should I reinstall?
Should you decide not to follow that advice, we will do our best to help clean the computer of any infections but we cannot guarantee it to be trustworthy or that the removal will be successful. Let me know how you wish to proceed.