Harder levels:
If you set the virus level to 20 and complete it, you will start at the next level, level 21. The levels will keep increasing. However, when you get to level 35, it will reach the maximum number of viruses, leaving only two free rows of space to drop the pills. Note: Even after completing the higher levels, you must re-access them by completing level 20, then level 21, etc.
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