1.   A virus had infected the entire computer network.

2.   Before a virus can infect an animal cell it must first bind to specific receptor molecules embedded in the cell membrane.

3.   This virus infected thousands of computers within days.

4.   The virus has infected many people.

5.   The virus has infected many computers.

6.   Even then, a very new virus can infect your users.

7.   Although the other pox viruses can infect several different species, smallpox is a disease of humans only.

8.   Although West Nile virus mainly infects birds, it can be transmitted to humans by mosquitoes.

9.   And a protease inhibitor, which blocks the protease enzyme needed for the HIV virus to infect other cells, may not even be necessary.

10.   Animal research also is difficult because chimpanzees, which are scarce and difficult to study, are the only animals the virus can infect other than humans.