Screensavers

Early computers used cathode ray tubes (CRTs) for display. These were basically analog TV sets designed to work with a computer video system. The CRT works by scanning an electron beam across a phosphor screen to illuminate small spots (pixels) and thus create text and graphics. If an static image was displayed for long periods of time on a CRT, the phosphor tended to “burn-in” and a ghost of that static image would appear in the background of whatever else was subsequently shown on the screen. Screensavers were created to help solve this problem by sitting the background and, after some period of inactivity, activating to show some moving image(s) on the screen and thus avoid the burn-in problem.

CRTs today have less of a problem with burn-in because phosphor coatings have improved and images are not the stark on or off of earlier computers. Plasma displays can also suffer from some burn-in symptoms but these generally are not used for computer displays. LCDs, while not having a burn-in problem, do suffer from a form of image persistence that a screensaver can’t really address. Since many computer displays are LCDs today and those with CRTs have the advanced phosphors screensavers are now more of an interesting addition instead of a needed utility and, thus, are mostly entertainment related. Some screensavers even perform useful tasks by joining in massive parallel computing tasks to process massive amounts of data. Examples include analysis of SETI data and analysis of protein folding.

The important thing to note about the above is that screensavers are basically just executable programs which may be just renamed EXE files (a screensaver will often have the extension .SCR). As programs, screensavers are vulnerable to infection just like any other program. Despite the fact that programs today often have security certificates attached, all the certificates do is verify an identity which may be meaningless relating to infection.

Indeed, in 2006, the BBC reported that “…the most dangerous words to search for are ‘free screensavers’.” 64% of the sites returned were reported to have features that caused users problem.

As with all programs, be careful with screensavers and know your sources if you get one.

What Viruses Infect
Visual Basic Files	Vulnerabilities