Home > Computers and Internet > LSASS.EXE Infection Very Disruptive

LSASS.EXE Infection Very Disruptive

15-Apr-05 06:46 pm EDT Leave a comment Go to comments

Not sure which trojan was responsible for this, but I installed an infected crack utility recently, which I’ve done with increasing frequency of late.  I’m relying on a number of utilities I’ve installed and keep regularly updated to "catch" any infections as or before they happen.  I always scan, etc. before using anything downloaded from a questionable source.

But I got taught a lesson this past week.  Neither McAffee VirusScan, SpyDoctor nor Microsoft’s AntiSpyware utilitity caught something that infected the LSASS.EXE file on my main instance of Windows XP.  This file is used by Windows to handle local authentication, among other things and without it – your computer can do anything from become a node of denial-of-service (DOS) attacks, to staying pinned at 100% CPU use, to stop working entirely.

In my case it was all of the above.

I had a brief opportunity to try and cleanse the file once I realized what was wrong, but none of the additional utilities I thew at it initially worked, nor did a rogue process appear in the process list.  Once I couldn’t login I hacked away at it for hours – unable to login or do anything with the infected system.

Eventually, it dawned on me to simply take a non-infected copy of LSASS.EXE and put it on the system.  But I guess I’m kinda old-school still.  I didn’t realize that the WinXP CD comes with a "Recovery Mode" that allows you to get an MS-DOS prompt and copy files over with floppies or CD-ROM.


But, the thought occurred: what if one doesn’t have another instance of WinXP?  My online search did reveal one site (http://www.allbootdisks.com) that carries installable instances of every Windows OS, and images of older MS DOS versions, from which the installation binaries & files could be downloaded.  Not sure if this site’s legal, but assuming nobody comes along to shut it down, it’s a very useful recovery tool.  Of course – you need a system on which to install the files should disaster strike you as it did me.

Insidentally, as of right now the ProcessLibrary.com website is reporting that LSASS.EXE is the most popular file queried by site visitors – which indicates something’s up with this file for a lot of people at the moment.  Wonder if we’ll see any security advisories about worms or viruses that hit this file soon…..

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