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.
Viruses and worms are defined by their behaviour â malicious software designed to spread without the userâs knowledge. A virus infects legitimate software and when this software is used by the computer owner it spreads the virus â so viruses need you to act before they can spread.omputer worms, on the other hand, spread without user action. Both viruses and worms can carry a so-called âpayloadâ â malicious code designed to do damage. Trojans and Rootkits â the masked threat. Trojans and rootkits are grouped together as they both seek to conceal attacks on computers.