A does can exist. Like their executable counterparts, many macro viruses change their appearance to avoid scanning detection. Random encryption routines are used to hide the virus code, but the cipher routines tend to be weaker than their executable virus counterparts.
Some viruses randomly rename the macro names and memory variables. Others create their macros on the fly. They do this by storing most of the macros as plain text within the document, and calling a built-in macro builder.
The macro builder then builds the macros and executes them. One of the scariest mechanisms a macro virus can contain is a routine to install a more dangerous virus or Trojan. Although most macro languages limit the scope of what can be manipulated by the application, sophisticated macro languages like WordBasic and VBA allow the external file and operating system to be modified.
VBA and WordBasic allow external files to be created and existing files to be deleted or modified. Many macro viruses create a text file containing hexadecimal byte codes assembly language commands on a user's hard drive, and then modify the AUTOEXEC.
EXE is called to compile the text file and convert it to an executable, and then it is executed. Thus, an even more malicious virus or Trojan can attack a computer. And all the user did was open a Word document sent by a friend or coworker. An early macro virus named Nuclear was the first to including a virus dropper although the first versions were too buggy to work. EXE to spread a virus code is deliberately crippled. If you see code resembling the example above, you can be almost percent sure it is a virus or Trojan.
VBA contains plenty of functionality to allow macro viruses to interact with the PC outside of the scope of the application. Here are a few examples:. These four example commands can make any PC vulnerable to numerous types of attack.
Because macro viruses can contain many of the same macro names, such as AutoOpen or FileSaveAs , it is not uncommon for a document infected with two different macro viruses to end up creating a new virus that includes routines from each of the former. Here are some representative sample descriptions that demonstrate the versatility of macro viruses. This Melissa variant attempts to format local hard drives and corrupts CMOS memory, along with using email clients to forward itself.
BAT , that contains the following the commands that will format hard drives:. This command is repeated for drives D thru Z. BAT file to run a dropped malicious file, Y2K. This executable file will attempt to corrupt your CMOS settings disabling the hard drive, etc. Marker is a Word macro virus that keeps track of who it infects and transmits this information to a well-known hacker site now closed. SYS file contains the virus code and the.
EXE to send information back to the hackers. VXD file contains the commands in the example below:. It also disables Word's macro warning prompt. It keeps track of the user information found in Word's User Name and User Address information fields. Thus, anyone infected can usually find out who infected them and trace the origin of the virus back several generations. If so, it doesn't do it again. Although ACME conjures up images of roadrunner cartoons, it is a valid subkey name coded by Microsoft and not by the virus.
Example below shows a log file provided in an example I received names and addresses have been changed to protect the innocent :. The Codebreaker group released another intriguing macro virus. This one attempts to steal users' PGP private keys. PGP , or Pretty Good Privacy , is one of the world's most popular data and email encryption programs. PGP users have a private encryption key that is used to do the encrypting.
It is encrypted itself, but usually protected by a weak password. When loaded, it checks to see if the current Word document or global template contains a class module called Caligula.
If not, it exports its source code to a file called IO. VXD , and imports it to the global template. On the 31 st of any month, it will display a message saying "No cia, No nsa, No satellite, Could map our veins.
It looks for the value, Caligula. Even on users' systems without PGP, the virus will keep on replicating like any normal macro virus. I'm not sure of the legal reasons, but many computer security experts said this macro virus action the stealing of a user's private encryption key did not violate U.
Luckily, the Codebreakers web site was shutdown in an unrelated hunt for the Melissa virus writer. Triplicate is a common macro virus and the first cross-platform virus to infect three applications: Word, Excel, and PowerPoint. It infects the global template in Word, places an infected workbook called BOOK1 in Excel's Startup directory, and creates a new macro module called Triplicate in Powerpoint.
Triplicate was initially placed on a virus writer's web site, hidden in a web link. If a user clicked on the web link, it would load an infected document. In many cases, it would load in Word from within the browser without setting off any macro virus warnings. It does a simple file search for new victim files files with. CSC extension and the appropriate attributes. Most of the newer versions of Office 97 and later will warn you if a document, workbook, or datafile contains macros with the following message:.
Macros may contain viruses. It's much worse than that. What you need to look at is the percentage increase. In this case, it doubled an increase of percent in two days. At that rate, it will grow from 8, on Wednesday to 16, on Friday, and 32, by Sunday.
Maybe this popular parable will give you a feel for exponential growth: A kid wants to boost her allowance, and she proposes an unusual deal. Her parents would pay her daily, but the amount is only 1 cent today. Then it increases: 2 cents the next day, 4 cents the next—you get the idea. Small change, right? So how do you model the spread of a viral infection? And why is it called exponential growth anyway? Let's start with some basics.
Suppose we have a population, and a certain number N of them are carrying the Covid virus. When N is 1,, there will be new cases the next day. When N is 10,, there will be 2, new cases the next day. But here's the crazy part: This is like a car that is moving, but the speed depends on where it is. The farther it goes, the faster it goes. In this analogy, the distance traveled is like the number of people infected. You can obtain a formula for N as a function of time analytically using differential equations , but let's solve it numerically first.
Oh, a numerical calculation is where you break the problem into small time steps. At each step, I will calculate the number of infected people and from that calculate the number for the next day.
Using the rate of change formula above, I get the following infected update expression:. Disclaimer The funders had no role in experimental design, data analysis and interpretation or the decision to submit the work for publication. Provenance and peer review Not commissioned; externally peer reviewed. You will be able to get a quick price and instant permission to reuse the content in many different ways. Skip to main content. Log in via OpenAthens.
Log in using your username and password For personal accounts OR managers of institutional accounts. Forgot your log in details? Register a new account? Forgot your user name or password? Search for this keyword. Advanced search. Log in via Institution. You are here Home Online First Bacterial biofilms predominate in both acute and chronic human lung infections.
Email alerts. Article Text. Article menu. Respiratory infection. Original research. Bacterial biofilms predominate in both acute and chronic human lung infections. Abstract Background A basic paradigm of human infection is that acute bacterial disease is caused by fast growing planktonic bacteria while chronic infections are caused by slow-growing, aggregated bacteria, a phenomenon known as a biofilm.
Data availability statement Data are available upon reasonable request. Statistics from Altmetric. What is the bottom line?
Why read on? Introduction In the planktonic form, bacteria appear as single cells, whereas in the sessile form, bacteria are organised into multicellular aggregates, commonly referred to as biofilm. Materials and methods Additional methods are presented as online supplemental material.
Supplemental material [thoraxjnlsupp Figure 1 Flow chart of study and final diagnoses of patients recruited. Preparation, staining and microscopy of sputum specimens Sputum specimens measuring 4.
Baseline characteristics of patients Patient characteristics on admission are described in table 1. View this table: View inline View popup. Table 1 Characteristics of 43 patients with lower respiratory tract infection. Figure 2 Biofilms and planktonic cells are observed across infection types. Growth estimates based on fluorescence in sputum samples PNA-FISH has the added benefit of providing quantitative information regarding the number of ribosomes within a cell, which can be used as an indirect measurement of metabolic activity.
Figure 3 Estimation of bacterial growth rate based on fluorescence intensity. Inflammatory cell distribution and degree of inflammation Quantification of DAPI-stained inflammatory cells revealed no significant difference between inflammatory cell biomass in the three patient categories see figure 4A. Figure 4 Host cell biomass in all infection types.
Discussion The first study to describe the difference between acute and chronic infection was published by Marrie et al. Ethics statements Patient consent for publication Consent obtained directly from patient s.
Clin Microbiol Infect ; 21 Suppl 1 : S1 — OpenUrl PubMed. Biofilms in chronic infections - a matter of opportunity - monospecies biofilms in multispecies infections. Pseudomonas aeruginosa displays multiple phenotypes during development as a biofilm. J Bacteriol ; : — Insight into the microbial multicellular lifestyle via flow-cell technology and confocal microscopy.
Cytometry A ; 75 : 90 — Biofilm formation by Pseudomonas aeruginosa wild type, flagella and type IV pili mutants. Mol Microbiol ; 48 : — There is no hiding if you Seq: recent breakthroughs in Pseudomonas aeruginosa research revealed by genomic and transcriptomic next-generation sequencing.
J Med Microbiol ; 69 : — Stewart PS. Theoretical aspects of antibiotic diffusion into microbial biofilms. Antimicrob Agents Chemother ; 40 : — Tolerance of dormant and active cells in Pseudomonas aeruginosa PA01 biofilm to antimicrobial agents. J Antimicrob Chemother ; 63 : — Bactericidal effect of colistin on planktonic Pseudomonas aeruginosa is independent of hydroxyl radical formation. Int J Antimicrob Agents ; 43 : — 7. Denitrification by cystic fibrosis pathogens - Stenotrophomonas maltophilia is dormant in sputum.
If you find anything, you can remove it manually. As with all forms of computer viruses and malware, prevention is best. Use the following tips to help protect your computer:. Macro viruses are among some of the sneakier ways of infecting a computer. But there are things you can do to help protect your computer and data. All rights reserved. Firefox is a trademark of Mozilla Foundation. App Store is a service mark of Apple Inc.
Alexa and all related logos are trademarks of Amazon. Microsoft and the Window logo are trademarks of Microsoft Corporation in the U. The Android robot is reproduced or modified from work created and shared by Google and used according to terms described in the Creative Commons 3. Other names may be trademarks of their respective owners.
Security Center Malware Everything you need to know about macro viruses. Virus warning signs: How to tell if your computer has a virus Computer viruses are about as diverse as computer users. Read More.
0コメント