Threat description




Lebreat.m is a mass mailer and network worm spreading through a vulnerability in Windows Plug and Play service (MS05-039).


Automatic action

Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.

More scanning & removal options

More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.

You may also refer to the Knowledge Base on the F-Secure Community site for more information.

Contact Support

F-Secure customers can request support online via the Request support or the Chat forms on our Home - Global site.

Technical Details

The worm is a packed PE executable file 61291 bytes long.

Installation to system

When run, the worm copies itself under %SYSTEM% directory using the name 'winhost.exe' and creates mutexes named:

_-oO]xX|-S-k-y-N-e-t-|Xx[Oo- MuXxXxTENYKSDesignedAsTheFollowerOfSkynet-D

to make sure it only runs one copy of the worm at the same time.

Then it adds the following registry entries to ensure that it is started when a user logs on or the system is restarted:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "winhost" = "winhost.exe"

The worm will modify the hosts file in order to prevent the local users from accessing antivirus vendors' websites.

Spreading using Plug and Play service vulnerability

The worm scans for systems vulnerable to Microsoft Windows Plug and Play service (MS05-039) through TCP/445.

It creates several threads that connect to random IP addresses. If the exploit is successful the worm will spread to those hosts.

Please see the following page for detailed information on the vulnerability:


Email Spreading

The worm will also spread by email. The messages will be composed from different string within the worm's body. Subjets will be chosen from:

"Re: Msg reply"  "Re: Hello"  "Re:"  "Re: Yahoo!"  "Re: Thank you!"  "Re: Thanks :)"  "Re: Text message"  "Re: Document"  "Incoming message"  "Re: Incoming Message"  "Re: Incoming Msg"  "Re: Message Notify"  "Notification"  "Changes.."  "Update"  "Fax Message"  "Protected message"  "Re: Protected message"  "Forum notify"  "Site changes"  "Re: Hi"  "Encrypted document"   

The bodies for the messages will be selected among the following possibilities:

"Read the attach."  "Your file is attached."  "Try this."  "More info is in attach"  "See attach."  "Please, have a look at the attached fil"...  "Your document is attached."  "Please, read the document."  "Attach tells everything."  "Attached file tells everything."  "Check attached file for details."  "Check attached file."  "Pay attention at the attach."  "See the attached file for details."  "Message is in attach"  "Here is the file."   

The attachment names will be composed with any of:

"Details.doc"  "doc"  "Info.doc"  "Information.doc"  "Message.doc"  "MoreInfo.doc"  "Readme.doc"  "Updates.doc"  "text_doc"   

Followed by a sequence of whitespaces and the ".exe" extension appended to the end.

Other details

Lebreat.m modifies system hosts file in order to disable access to certain sites. Following hostnames are redirected to localhost IP address (

www.ca.com  pandasoftware.com  www.nai.com  kaspersky.com  www.f-secure.com  download.mcafee.com  tca.com  www.my-etrust.com  www.kaspersky.com  www.sophos.com  sophos.com  mcafee.com  www.mcafee.com  symantec.com  www.pandasoftware.com  www.sarc.com  trendmicro.com  f-secure.com  liveupdate.symantec.com  us.mcafee.com  www.symantec.com  www.trendmicro.com  

Detection Type: PC

Database: 2005-08-25_01

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