Virus Venn Diagram
Virus Venn Diagram
[Euler diagram with two circles that don't intersect. One circle is green, while the other is slight dark blue.] Green circle: Computer problems that make people say "Maybe it has a virus?" Blue circle: Computer problems caused by viruses

Randall uses an Euler diagram (technically not a Venn diagram ) to make fun of clueless computer users. The circles in the diagram don't overlap, meaning problems that people suspect are caused by viruses are never really caused by viruses, and problems that are actually caused by viruses are never suspected by people to be caused by a virus.
When computers don't function as expected, a common response from ordinary users is "Maybe it has a virus ?".  However, most of these situations can be explained by faulty hardware (freezing, blue screen, etc.) or software (crashes, errors, apparent lack of response to input, etc.), a general lack of maintenance (too slow to start up, too much clutter on screen, etc.), or user error.  A virus can potentially cause those symptoms, but it's much more common for them either to cause immediate and massive damage (rendering the computer completely unusable, wipe the disk, display obvious propaganda, etc.), or to remain stealthy with no obvious symptoms (logging keystrokes, exfiltrating sensitive information, receiving commands in the background, etc.).  Of course there is no clear separation and there is always some overlap between the two scenarios, so the diagram is not meant to be taken literally.
The title text refers to the technological singularity , a hypothetical point in the future when superintelligence emerges in computers, so that they can build new computers with ever increasing intelligence. It is seen as impossible to predict what would happen beyond this point; hence the term "singularity". 1084: Server Problem makes a joke on this.
"Defragging" is short for disk defragmentation , an easy, user-friendly action that PC users can undertake to supposedly make their computers run faster. It is therefore a common all-round recommendation to do this, regardless of the problem. Randall suggests the same clueless users would encounter the singularity and attempt defragging. It probably won't help much.
[Euler diagram with two circles that don't intersect. One circle is green, while the other is slight dark blue.] Green circle: Computer problems that make people say "Maybe it has a virus?" Blue circle: Computer problems caused by viruses
