The "Conficker" and "Taterf" computer worms are still going strong a year after they made their first appearances, U.S. experts say.

Eric Sites, chief technology officer of anti-virus firm Sunbelt Software, told Monday's USA Today the viruses may be unstoppable, but observed, "The sad fact is worms and viruses would be wiped out if everyone used best security practices."

The ability of the worms to spread their Internet-borne thievery of personal data and passwords and promulgate the sale of worthless software is escalating as U.S. software giant Microsoft sclosed the number of copies of Conficker and Taterf cleansed from Windows-based personal computers rose 98.4 percent in the first six months of this year, the newspaper reported.

"We're doing proprietary things with real dollars attached, raising the opportunity for people to take advantage," Rob Housman, executive director of the Cyber Secure Institute, told USA Today. "We didn't design the Internet to be secure. We designed it to be free."

Experts say the worms are spread when infected memory sticks, music players, cameras, camcorders and smartphones are plugged into the universal serial bus, or USB, ports of modern PCs.