1 Stress echocardiogram: This is an echocardiogram that is performed while the person exercises on a treadmill or stationary bicycle. 2  This test can be used to visualize the motion of the heart's walls and pumping action when the heart is stressed.
Viruses require an active host program to cause damage and infect other executable files or documents, while worms are stand-alone malicious programs that can self-replicate and propagate via computer networks, without human help.
Unlike viruses, worms do not have to attach themselves to a program in your computer, and may not damage files on an infected computer. Instead, worms more often slow down computer networks by eating up bandwidth, or your computer's ability to prcess data, as the malware replicates and spreads.iruses can enter your computer in any number of ways, such as via an email attachment, during file downloads from the Internet or even upon a visit to a contaminated Web site.